A Kaleidoscopic Navigation Through Different Shades of Colors in Dermoscopy

Dermoscopy has traveled a long way from its initial application limited to tumoral dermatology, especially melanocytic tumors, to its indispensable role in general dermatology as well as in procedural dermatology. Dermoscopy primarily serves as a diagnostic tool by virtue of its ability to visualize skin surfaces and sub-surface structures in a magnified and illuminated manner. Colors are critical and significant in dermoscopy. They are imparted by different chromophores in skin tissue. Hence, recognition of diverse colors and their variations is of paramount importance in the analysis of a dermoscopic image. In this review, we describe the various colors observed in dermoscopy, emphasizing the same in order to interpret them appropriately for an accurate diagnosis


Introduction
I nitially used in the diagnosis of skin tumors, especially melanocytic tumors, the role of dermoscopy in general dermatology has evolved to a great extent.Dermoscopy primarily serves as a diagnostic tool by its distinct ability to visualize skin surfaces and sub-surface structures in a magnified and illuminated manner.One of the important elements in dermoscopic diagnosis is the colors exhibited by the lesions reflecting the underlying tissue involved.In this review, we describe the various colors observed in dermoscopy with an emphasis on the basis of the same in order to interpret them appropriately for an accurate diagnosis.

The instrument
Dermoscope is the tool, and dermoscopy is the method.Dermoscopes can be hand-held with 10-fold magnification and the facility to capture images.The instrument consists of an achromic lens, in-built light emitting diodes (LED) lamps, and a power supply.Lenses provide magnification, and LEDs act as light sources (Figure 1a).Hand-held dermoscopes need to be attached to a smart phone to capture and save the images (Figure 1b).A videodermoscope with magnifications from 20 x to 160 x to 220 x, allows simultaneous visualization of images on the monitor screen, and these images can be saved (Figure 2).

Principle
The eyes cannot perceive the structures that are subsurface in the skin.This is largely due to reflection, refraction, scattering, and the absorption of light.These factors are reduced to a greater extent by the achromic lens, the use of the interface medium, and polarized light.The achromic lens reduces the refraction between the air and stratum corneum, while the interface medium decreases the specular reflection.Polarization mode modifies the scattering and absorption of light so that the deeper structures are made visible (Figure 3). 3 The illumination in dermoscopy is achieved by different light sources, such as non-polarized, polarized, blue light, or UV light.The dermoscopic features thus observed reflect the histological aspects of the skin lesion and hence assist in a more accurate clinical diagnosis of the same.The dermoscopic features observed are described in terms of structures and their morphology, the patterns formed by the structures and the various colors imparted by the structures ,and patterns.

Basic structures and patterns
The basic structures in dermoscopy include the dot, clod, line, circle, pseudopod, and structureless area.Dot-a non-measurable point-like solid object; clodsolid object bigger than the dot with variable color and shape; line-structure with length greater than width; pseudopod-a line with a bulbous end; and structureless area-an area that covers 10-25% of the field without identifiable basic structures. 4These structures are basically described from the perspective of pigmented lesions, especially melanocytic lesions.They form the language of dermoscopy.Each lesion is described using these terms to maintain uniformity for better understanding and learning dermoscopy.Multiple repeats of the structures form the patterns in dermoscopy.

Description of a lesion
The dermoscopic features observed are described in terms of structures and their morphology, the patterns formed by the structures, and the various colors imparted by the structures and patterns.The colours are the main determinants of dermoscopic diagnosis as they reflect the tissue involved in the pathology, or the tissue alterations/reactions.A given lesion is analyzed and described based on the following parameters; background color (white, brown, black, or pink), pigmented structures (pigment network, grey clods, brown clods), follicular changes (follicles ostia present or absent, dilated follicular openings, follicular plugs), scales (morphology and distribution, [focal, eccentric, perifollicular, diffuse]), vascular elements (morphology and distribution) and a special clue. 5

Determinants of basic color in dermoscopy
The colors in dermoscopy are determined by the tissue chromophores.The three essential chromophores in the skin are keratin, melanin, and haemoglobin.White, black, and red are primarily imparted by keratin, melanin, and hemoglobin respectively.However, these colors are not exclusive to them, and certain other tissue elements or alterations can impart similar colors as outlined in Table 1 and depicted in Figures 4-6

Determinants of different shades of basic colors in dermoscopy
The basic colors described above can have different variants.The variations are determined by various factors, as described in Table 2 and depicted in Figures 7-9.
As with the basic colors, the variants of the basic colors can also be imparted by other tissue elements or alterations, as delineated in Table 3       It is hence of paramount importance to interpret the colors contextually.Colours in dermoscopy other than the basic colors and/or their variations most likely represent exogenous factors (e.g., tattoo pigment) or certain optical phenomena as described below.

Rainbow phenomenon
The rainbow phenomenon (RP) is seen as multicoloured pattern in dermoscopy and does not have a specific corresponding change in histopathology.
Earlier, it was thought to be specific for Kaposi sarcoma.However, it is found in many dermatoses, including lichen planus, dermatofibroma, melanoma, acroangiodermatitis, etc. 8 It is thought that RP is because of microscopic vascular structure, as it was observed in vascular tumors.Recently, RP has been found in non-vascular lesions, explaining the role of the optical phenomenon of polarized light.It is not seen with non-polarized light, with or without an interface medium.Hence, it is a complex and intricate process that takes place when polarized light traverses and interacts with the vascular and other structures of the skin.The multicolored pattern is due to the interplay of different states of polarization of light with absorption and interference of colors. 9The histopathological correlation of this dermoscopic feature is not established. 10s mentioned earlier, RP is increasingly found in many vascular and non-vascular dermatoses, diagnosis should not be counted only on the presence of RP; rather ,other relevant dermoscopic features and clinical context are taken into consideration.RP is observed in basal cell carcinoma (Figure 13a), dermatofibroma, pyogenic granuloma (Figure 13b), malignant melanoma, etc. 8,11 Auroa borealis This pattern is exclusively observed in onychomycosis.
It produced, as a result of onycholysis, longitudinal spikes and striae and multiple colors of chromonychia (Figure 14).The name Aurora borealis is derived from light waves in the northern hemisphere because of its appearance.It should be noted that this pattern is specific and sensitive to onychomycosis. 12

Blue-white veil
Blue-white veil (BWV) is a confluent blue pigmentation over the underlying ground-glass haziness.It is due to the combination of compact orthokeratosis with heavily pigmented and aggregated melanocytes, melanophages, or melanin in the dermis. 13Although it is characteristically seen in melanoma, few conditions, such as blue nevus (Figure 15a) and basal cell carcinoma (BCC) (Figure 15b) display this feature.
In melanoma, it is always focal and nonuniform in nature (Figure 15c) as compared to other benign conditions such as blue nevus, wherein BWV occupies entire lesion.The presence of BWV in BCC has been reported recently.Studies from the Indian population showed the occurrence of BWV in 57.3% and 53.4% of patient with micro-nodular and nodular variants respectively. 11,14 t is noted in pigmented variants of BCC.Obviously, heavily pigmented tumor cells and orthokeratosis, and epidermal hypergranulosis contribute to BWV.Interestingly, BWV is also found in BCC without hypergranulosis and orthokeratosis.The authors are of the opinion that BWV is due to heavily pigmented melanophages and fibrosis between the stroma and tumor cells. 15Hence, further studies are recommended to validate BWV in BCC in terms of its histopathological correlation.Furthermore, regressing lesions also demonstrate blue-grey areas, which are difficult to distinguish from BWV.It is documented that BWV is frequently observed in palpable lesions, whereas blue-grey areas are noted in atrophic or flat lesions.Interestingly, diffuse light brown pigmentation is associated with blue-grey areas and not seen with BWV. 16g 13   Rainbow phenomenon is also seen in basal cell carcinoma (yellow rectangle).

Polarized and non-polarized light
Polarized (PD) and non-polarized (NPD) lights are used in dermoscopes, and they complement each other.NPD mode with an achromic lens reduces the surface glare, and with an interface medium (ultrasound gel or isopropyl alcohol), it allows deeper penetration of light and visibility of subsurface structures up to the dermo-epidermal junction.Whereas PD mode uses cross-polarization to prevent contact with skin lesions and visualize deeper structures up to the reticular dermis. 3,17 lood vessels and pink color are well visualized in PD due to the lack of pressure effect (non-contact) and deeper location of vessels in the skin layers.Additionally, pigmented lesions with pigment in the dermo-epidermal junction show darker shades of brown and blue as compared to NPD. 18 PD and NPD demonstrate minute differences in the structures that assist in an accurate diagnosis.For example, amelanotic or structure-poor melanoma is better seen with PD, and comedo-like openings and milia-like cysts are better appreciated with NPD.Now-a-days, all scopes have the inbuilt facility of both polarized and non-polarized lights.Thus, just toggling between the two will show the differences even better with both PD and NPD.This is referred to as a blink sign as structures blink at you when you toggle between PD and NPD.There are a few examples of polarized and non-polarized light dermoscopy, as follows.Scales appear prominent in NPD (Figure 16a) as compared to PD (Figure 16b).Similarly, follicular plugs are better visualized in NPD than in PD (Figure 17).The pink area is better appreciated in PD than in NPD (Figure 18).Fluid in the vesicular lesion is easily visible with PD (Figure 19a), while the surface is well appreciated in NPD (Figure 19b).Dermal melanin is readily visible in PD (Figure 20a),while it is not appreciated with NPD (Figure 20b).Hence, the color of melanin appears brown or gray if it presents in the epidermis and dermis, respectively (Figure 8).White rosettes and white shiny streaks are prototype features that are better visualized only in polarized dermoscopy.The former appears as four white clods meeting at a center point (Figure 21) and it represents hyperkeratotic dilated infundibulum, while the latter is due to collagen in the dermis, seen as whitish shiny strands (Figure 22).White rosettes are non-specific and noted in many dermatoses, including discoid lupus erythematosus. 19onditions with increased collagen demonstrate white, shiny streaks. 20

Parallel polarisation
It is a new addition to the dermoscope.Here, two polarizing filters are placed in the same direction so that polarized light reflected from the skin surface is allowed to traverse the second filter, which is helpful in visualization of surface and subsurface structures (Figure 23a).probably gives more details of superficial structures than the non-polarized light (Figure 23b).Cross polarization has two filters in 90 0 in which polarized light reflected from the skin surface is blocked by a second filter, permitting only non-polarized light (light that loses its polarization in deeper layers of skin) reflected from deeper layers.It is better utilized in the visualization of deeper structures (Figure 23c). 21

Blue light
Blue light is incorporated into a multispectral dermoscope because of its wavelength of 470nm, which is absorbed by melanin.As compared to white light, sharp borders in stable vitiligo are well demarcated by blue light (Figure 24).In contrast, spreading borders are not visualized better with blue light.Thus, blue light differentiates stable and unstable vitiligo by increasing the contrast between areas with melanin and those without melanin. 22

Yellow light
Yellow light in ultraviolet spectrum has higher wavelength and it penetrates deeper in dermis.Hence, it matches with absorptive spectrum of melanin and hemoglobin.The lesions with more vasculature and dermal melanin are visualised better with yellow light.They stand-out well against a yellow background.Yellow light, similar to blue light is incorporated in multispectral dermoscope by DermLite.Vessels in rosacea (Figure 25), dermal melanin in pigmented contact dermatitis and nail fold capillaries are well visualised with yellow light. 23

Ultraviolet light
Recently, the facility of an ultraviolet (UV) light source with 365nm was introduced in dermoscopy.It is akin to the basic physics of using Wood's lamp.This technique is based on the Stokes shift phenomenon, which describes that UV light stimulates fluorescence by skin chromophores, thereby detecting particular fluorescents in a given skin lesion. 24,25 ccordingly, UV fluorescent (UVF), induced dermoscopy gives an additional clue to many non-neoplastic dermatoses.UVF dermoscopy shows characteristic fluorescence in inflammatory, infective, and pigmentary dermatoses. 24Erythrasma demonstrates coral red fluorescence in a polygonal pattern (Figure 26), and vitiligo shows no fluorescence (Figure 27).In the herpes zoster, green and purplish fluorescence are noted in the center and periphery respectively (Figure 28).Bullous pemphigoid reveals green fluorescence (Figure 29).

Conclusion
Dermoscopy serves as a very useful auxiliary tool in the clinical diagnosis of skin lesions.The colors of the structures and patterns in dermoscopy are the main determinants of the pathological aspects of the skin lesion, and awareness about the appropriate and contextual interpretation of the same is imperative to optimally apply dermoscopy as a diagnostic tool.

Figure 1 :
Figure 1: (a) Hand held dermoscope with power button (black arrow), polarized and non-polarized knob (red arrow), brightness enhancing knob (yellow arrow) and faceplate of dermoscope (blue

Figure 3 :
Figure 3: Schematic diagram depicting the physics of cross polarization.Source and detector polarizers are placed perpendicularly.Detector polarizer allows nonpolarized absorbed light from the skin surface that has lost its phase or polarization (green arrow) whereas it blocks the reflected polarized light that has retained its phase or polarization (yellow arrow).[Reused with permission from editor-in-chief; Ankad BS, Smitha S V, Koti VR.Basic science of dermoscopy.Clin Dermatol Rev 2020; 4:69-73] .

Figure 4 :
Figure 4: White color in dermoscopy of keratin (a) in a keratinizing lesion, dermal sclerosis (b) and atrophy in lichen sclerosus et atrophicus (c), and amelanosis (d) in vitiligo.Figure 5: Black color in dermoscopy of melanin (a) in a melanocytic lesion and of deoxygenated blood (b) due to thrombosed vessels in a case of lymphangioma circumscriptum.Figure 6: Red color in dermoscopy of haemoglobin (a) in a pyogenic granuloma and red-pink background color of collagen (b) in an eroded skin lesion.

Figure 5 :
Figure 4: White color in dermoscopy of keratin (a) in a keratinizing lesion, dermal sclerosis (b) and atrophy in lichen sclerosus et atrophicus (c), and amelanosis (d) in vitiligo.Figure 5: Black color in dermoscopy of melanin (a) in a melanocytic lesion and of deoxygenated blood (b) due to thrombosed vessels in a case of lymphangioma circumscriptum.Figure 6: Red color in dermoscopy of haemoglobin (a) in a pyogenic granuloma and red-pink background color of collagen (b) in an eroded skin lesion.

Figure 6 :
Figure 4: White color in dermoscopy of keratin (a) in a keratinizing lesion, dermal sclerosis (b) and atrophy in lichen sclerosus et atrophicus (c), and amelanosis (d) in vitiligo.Figure 5: Black color in dermoscopy of melanin (a) in a melanocytic lesion and of deoxygenated blood (b) due to thrombosed vessels in a case of lymphangioma circumscriptum.Figure 6: Red color in dermoscopy of haemoglobin (a) in a pyogenic granuloma and red-pink background color of collagen (b) in an eroded skin lesion.

Figure 9 :
Figure 7: Different colors of keratin.Keratin appears yellow (black star) when it is dense and compact whereas loose and lamellated keratin imparts a white color (red star).Keratin admixed with serum appears yellow-orange (yellow star), with fresh bleed appears red (black arrow), with an old bleed appears black (white star) due to deoxygenation of the hemoglobin and brown when admixed with hemosiderin (red arrow) Figure 8: Different colors of melanin in melanocytic nevi.Melanin in stratum corneum and upper granular layer appears black (a), appears brown in Malpighian layer (b), grey to grey-blue at the level of papillary dermis and upper reticular dermis (c, yellow stars) and in deep reticular dermis melanin appears bluish due to Tyndall effect (c, white star).Figure 9: Different colors of haemoglobin in a case of lymphangioma circumscriptum.Oxygenated haemoglobin imparts a red color to the blood seen as red clods (black star) and deoxygenated blood in thrombosed vessels appears bluish-black seen as blue-black clods (yellow star).Figure 10: Yellow color imparted by various tissues such as sebaceous glands (a) in nevus sebaceous, fat (b) in nevus lipomatosus and pus (c) in inflammatory tinea as whitish-yellow color.Figure 11: Variations of yellow color such as yellow-orange is imparted by dense or granulomatous cellular infiltrate seen as a yellow-orange clod (black arrow) and sparse of non-compact cellular infiltrate appears yellow-white to white color (white arrow).Figure 12: Variations of red color such as (a) bright red imparted by extravasated red blood cells seen as red dots (black circle) and the extravasated red blood cells with inflammatory infiltrate appears as purplish as seen in the background (black star).(b) As the hemorrhage resolves, brown color develops seen as brown clods (black arrow) attributable to hemosiderin.

Figure 10 :
Figure 7: Different colors of keratin.Keratin appears yellow (black star) when it is dense and compact whereas loose and lamellated keratin imparts a white color (red star).Keratin admixed with serum appears yellow-orange (yellow star), with fresh bleed appears red (black arrow), with an old bleed appears black (white star) due to deoxygenation of the hemoglobin and brown when admixed with hemosiderin (red arrow) Figure 8: Different colors of melanin in melanocytic nevi.Melanin in stratum corneum and upper granular layer appears black (a), appears brown in Malpighian layer (b), grey to grey-blue at the level of papillary dermis and upper reticular dermis (c, yellow stars) and in deep reticular dermis melanin appears bluish due to Tyndall effect (c, white star).Figure 9: Different colors of haemoglobin in a case of lymphangioma circumscriptum.Oxygenated haemoglobin imparts a red color to the blood seen as red clods (black star) and deoxygenated blood in thrombosed vessels appears bluish-black seen as blue-black clods (yellow star).Figure 10: Yellow color imparted by various tissues such as sebaceous glands (a) in nevus sebaceous, fat (b) in nevus lipomatosus and pus (c) in inflammatory tinea as whitish-yellow color.Figure 11: Variations of yellow color such as yellow-orange is imparted by dense or granulomatous cellular infiltrate seen as a yellow-orange clod (black arrow) and sparse of non-compact cellular infiltrate appears yellow-white to white color (white arrow).Figure 12: Variations of red color such as (a) bright red imparted by extravasated red blood cells seen as red dots (black circle) and the extravasated red blood cells with inflammatory infiltrate appears as purplish as seen in the background (black star).(b) As the hemorrhage resolves, brown color develops seen as brown clods (black arrow) attributable to hemosiderin.

Figure 11 :
Figure 7: Different colors of keratin.Keratin appears yellow (black star) when it is dense and compact whereas loose and lamellated keratin imparts a white color (red star).Keratin admixed with serum appears yellow-orange (yellow star), with fresh bleed appears red (black arrow), with an old bleed appears black (white star) due to deoxygenation of the hemoglobin and brown when admixed with hemosiderin (red arrow) Figure 8: Different colors of melanin in melanocytic nevi.Melanin in stratum corneum and upper granular layer appears black (a), appears brown in Malpighian layer (b), grey to grey-blue at the level of papillary dermis and upper reticular dermis (c, yellow stars) and in deep reticular dermis melanin appears bluish due to Tyndall effect (c, white star).Figure 9: Different colors of haemoglobin in a case of lymphangioma circumscriptum.Oxygenated haemoglobin imparts a red color to the blood seen as red clods (black star) and deoxygenated blood in thrombosed vessels appears bluish-black seen as blue-black clods (yellow star).Figure 10: Yellow color imparted by various tissues such as sebaceous glands (a) in nevus sebaceous, fat (b) in nevus lipomatosus and pus (c) in inflammatory tinea as whitish-yellow color.Figure 11: Variations of yellow color such as yellow-orange is imparted by dense or granulomatous cellular infiltrate seen as a yellow-orange clod (black arrow) and sparse of non-compact cellular infiltrate appears yellow-white to white color (white arrow).Figure 12: Variations of red color such as (a) bright red imparted by extravasated red blood cells seen as red dots (black circle) and the extravasated red blood cells with inflammatory infiltrate appears as purplish as seen in the background (black star).(b) As the hemorrhage resolves, brown color develops seen as brown clods (black arrow) attributable to hemosiderin.

Figure 12 :
Figure 7: Different colors of keratin.Keratin appears yellow (black star) when it is dense and compact whereas loose and lamellated keratin imparts a white color (red star).Keratin admixed with serum appears yellow-orange (yellow star), with fresh bleed appears red (black arrow), with an old bleed appears black (white star) due to deoxygenation of the hemoglobin and brown when admixed with hemosiderin (red arrow) Figure 8: Different colors of melanin in melanocytic nevi.Melanin in stratum corneum and upper granular layer appears black (a), appears brown in Malpighian layer (b), grey to grey-blue at the level of papillary dermis and upper reticular dermis (c, yellow stars) and in deep reticular dermis melanin appears bluish due to Tyndall effect (c, white star).Figure 9: Different colors of haemoglobin in a case of lymphangioma circumscriptum.Oxygenated haemoglobin imparts a red color to the blood seen as red clods (black star) and deoxygenated blood in thrombosed vessels appears bluish-black seen as blue-black clods (yellow star).Figure 10: Yellow color imparted by various tissues such as sebaceous glands (a) in nevus sebaceous, fat (b) in nevus lipomatosus and pus (c) in inflammatory tinea as whitish-yellow color.Figure 11: Variations of yellow color such as yellow-orange is imparted by dense or granulomatous cellular infiltrate seen as a yellow-orange clod (black arrow) and sparse of non-compact cellular infiltrate appears yellow-white to white color (white arrow).Figure 12: Variations of red color such as (a) bright red imparted by extravasated red blood cells seen as red dots (black circle) and the extravasated red blood cells with inflammatory infiltrate appears as purplish as seen in the background (black star).(b) As the hemorrhage resolves, brown color develops seen as brown clods (black arrow) attributable to hemosiderin.

Figure 13 :
Figure 13: Rainbow phenomenon in (a) basal cell carcinoma and (b) pyogenic granuloma (yellow rectangle) with combination of multicolors like blue, red, yellow and purple.Figure 14: Onychomycosis shows multiple colors of chromonychia in aurora borealis phenomenon.Figure 15: Blue white veil as confluent bluish pigmentation covering entire lesion in (a) blue nevus and focal in (b) basal cell carcinoma and (c) malignant melanoma (yellow star).Rainbow phenomenon is also seen in basal cell carcinoma (yellow rectangle).

Figure 14 :
Figure 13: Rainbow phenomenon in (a) basal cell carcinoma and (b) pyogenic granuloma (yellow rectangle) with combination of multicolors like blue, red, yellow and purple.Figure 14: Onychomycosis shows multiple colors of chromonychia in aurora borealis phenomenon.Figure 15: Blue white veil as confluent bluish pigmentation covering entire lesion in (a) blue nevus and focal in (b) basal cell carcinoma and (c) malignant melanoma (yellow star).Rainbow phenomenon is also seen in basal cell carcinoma (yellow rectangle).

Figure 15 :
Figure 13: Rainbow phenomenon in (a) basal cell carcinoma and (b) pyogenic granuloma (yellow rectangle) with combination of multicolors like blue, red, yellow and purple.Figure 14: Onychomycosis shows multiple colors of chromonychia in aurora borealis phenomenon.Figure 15: Blue white veil as confluent bluish pigmentation covering entire lesion in (a) blue nevus and focal in (b) basal cell carcinoma and (c) malignant melanoma (yellow star).Rainbow phenomenon is also seen in basal cell carcinoma (yellow rectangle).

Figure 28 :
Dermoscopy of herpes zoster.(a) Clinical image, (b) white light dermoscopy reveals whitish globular structures with brown clods in the centre with reddish rim in the periphery.(c) Ultraviolet induced fluorescence dermoscopy shows greyish-white structures with purplish rim.

Table 1 :
Basic colors in dermoscopy

Table 2 :
Variations of the basic colors in dermoscopy

Table 3 :
Variations of the basic colors imparted by other tissues or tissue reactions