The Role of Subtractive Color Mixing in the Perception of Blue Nevi and Veins—Beyond the Tyndall Effect | Dermatology | JAMA Dermatology | JAMA Network
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Figure 1.  Reflectance Spectra of Normal Skin, Skin Overlying a Vein, a Normal Nevus, and a Blue Nevus
Reflectance Spectra of Normal Skin, Skin Overlying a Vein, a Normal Nevus, and a Blue Nevus

This graph shows the reflectance of a blue nevus, nevus, normal skin, and a vein across a spectrum of visible light ranging from 400 nm to 700 nm. The blue nevus shows a decreased red light reflectance compared with a normal nevus, and the vein shows a decreased red light reflectance compared with normal skin. Through the concept of subtractive color mixing, this decrease in red light contributes to a perceived blue hue.

Figure 2. Image Depicting the Concept of Simultaneous Contrast
Image Depicting the Concept of Simultaneous Contrast

This image demonstrates the concept of simultaneous contrast. Both eyes in A and B are exactly the same hue of gray (CMYK 55%, 53%, 48%, 16%). A, When 1 eye is peripherally surrounded by red, that same gray hue appears dramatically blue. B, This illusion is dispelled when the red is removed. Image adapted from Rootman et al.4

1.
Edwards  E, Duntley  Q.  The pigments and color of living human skin.  Am J Anat. 1939;65(1):1-33.Google ScholarCrossref
2.
Anderson  RR, Parrish  JA. Optical Properties of Human Skin. In: Regan  J, Parrish  J, eds.  The Science of Photomedicine. New York, NY: Plenum Press; 1982:147-194.
3.
Findlay  GH.  Blue skin.  Br J Dermatol. 1970;83(1):127-134.PubMedGoogle ScholarCrossref
4.
Rootman  DB, Lin  JL, Goldberg  R.  Does the Tyndall effect describe the blue hue periodically observed in subdermal hyaluronic acid gel placement?  Ophthal Plast Reconstr Surg. 2014;30(6):524-527.PubMedGoogle ScholarCrossref
5.
Kienle  A, Lilge  L, Vitkin  IA,  et al.  Why do veins appear blue? a new look at an old question.  Appl Opt. 1996;35(7):1151.PubMedGoogle ScholarCrossref
6.
Monnier  P.  Standard definitions of chromatic induction fail to describe induction with S-cone patterned backgrounds.  Vision Res. 2008;48(27):2708-2714.PubMedGoogle ScholarCrossref
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Research Letter
October 2016

The Role of Subtractive Color Mixing in the Perception of Blue Nevi and Veins—Beyond the Tyndall Effect

Author Affiliations
  • 1Division of Dermatology, University of California, Los Angeles, Los Angeles
  • 2Dermatology Service, Sacramento VA Medical Center, Mather, California
  • 3Keck School of Medicine, University of Southern California, Los Angeles
  • 4Department of Dermatology, University of California, Davis, Sacramento
  • 5Jules Stein Eye Institute and Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles
  • 6SUNY Downstate Medical Center Department of Dermatology, Brooklyn, New York
JAMA Dermatol. 2016;152(10):1167-1169. doi:10.1001/jamadermatol.2016.2201

The original study1 that proposed the “Tyndall effect” as the explanation behind the coloration of blue nevi drew from spectrophotometric data on cadaveric skin and not the direct study of blue nevi. Since then, the moniker of the Tyndall effect has been applied to a variety of blue phenomena in the skin despite a lack of confirmatory data. We hypothesized that other light-skin optical characteristics may provide a better explanation for the visual phenomenon associated with why blue nevi appear blue.

To briefly review the optics of the skin, perceived color is produced by light that strikes the skin and is remitted (a combination of light reflected and scattered back to the eye). The epidermis plays a minimal role in scattering, responsible primarily for the baseline reflectance of 5% to 7% of light from the skin surface.2 The Tyndall effect originally described the preferential scattering of shorter wavelength blue light through particulate matter in air and fluids, and its application to solid tissue optics is based on extrapolative hypotheses. Accordingly, such scattering would occur in a homogenous manner diffusely throughout the skin, not only in blue nevi, which led us to believe that the Tyndall effect does not fully account for the optics associated with blue nevi and veins.

Methods

We used a spectrophotometer (Konica-Minolta CM 2600d) to measure reflectance from (1) a normal and blue nevus and (2) a vein and comparable normal skin—each pair from the same authors. Telephone consultation with the Western Institutional Review Board (WIRB), Puyallup, Washington, determined this research to be exempt and institutional review board review was waived.

Results

Both types of nevi showed reflectance spectra similar to known melanin curves—with high absorption of blue light and decreased absorption of red light (Figure 1).2 The shorter wavelengths (approximately 400-500 nm) demonstrated the expected baseline reflectance off of the surface of the skin (8%), illustrating that the role of blue light scattering is minimal, and the amount of red-spectrum light is the main determinant of color. The spectral curves between vein skin and normal skin demonstrated similar decrease in red in the skin overlying a vein.

Discussion

The decrease in red light that yields the blue appearance of nevi and veins is accounted for through a concept termed “subtractive color mixing,” analogous to removing red out of purple paint.3 While the distinction between preferential blue scattering (Tyndall effect) or less red reflectance initially appears semantic, it recognizes that there are additional reasons beyond light scatter that can lead to decreased red reflectance, including differences in vasculature, hemoglobin levels, or characteristics of melanin (small structural differences can lead to changes in color, as seen in oxyhemoglobin vs deoxyhemoglobin).

In veins, the decrease in red color prompts a change in color perception.4,5 In this situation, the eye uses a type of chromatic induction called “simultaneous contrast” to enhance the contrast between 2 colors, leading the brain to perceive and interpret this lack of red as blue.4,6 The principle is illustrated in Figure 2A, where both eyes are exactly the same hue of gray (CMYK 55%, 53%, 48%, 16%), but when 1 eye is peripherally surrounded by red, that same gray hue appears strikingly blue. This illusion is dispelled when the surrounding red is removed (Figure 2B).

It is traditionally explained that the Tyndall effect leads to a preferential scattering and subsequent reflectance of blue light back to the eye, which accounts for the color of blue nevi. Blue nevi and veins are perceived as blue because they have less red, leading to a shift in hue toward blue (subtractive color mixing), an effect enhanced by chromatic induction because of the decrease in red relative to the surrounding skin.

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Article Information

Corresponding Author: Jared Jagdeo, MD, MS, Department of Dermatology, University of California Davis, 3301 C St, Suite 1400, Sacramento, CA 95816 (jrjagdeo@gmail.com).

Accepted for Publication: May 20, 2016.

Published Online: July 13, 2016. doi:10.1001/jamadermatol.2016.2201

Author Contributions: Drs Shive and Jagdeo had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Shive, Ho, Mamalis, Jagdeo.

Acquisition, analysis, or interpretation of data: Shive, Ho, Lai, Mamalis, Miller, Jagdeo.

Drafting of the manuscript: Shive, Jagdeo.

Critical revision of the manuscript for important intellectual content: Shive, Ho, Mamalis, Miller, Jagdeo.

Conflict of Interest Disclosures: None reported.

Additional Contributions: We are indebted to Randy Bunney, BS, Konica-Minolta, for his help with the data collection. He was not compensated for his contribution.

References
1.
Edwards  E, Duntley  Q.  The pigments and color of living human skin.  Am J Anat. 1939;65(1):1-33.Google ScholarCrossref
2.
Anderson  RR, Parrish  JA. Optical Properties of Human Skin. In: Regan  J, Parrish  J, eds.  The Science of Photomedicine. New York, NY: Plenum Press; 1982:147-194.
3.
Findlay  GH.  Blue skin.  Br J Dermatol. 1970;83(1):127-134.PubMedGoogle ScholarCrossref
4.
Rootman  DB, Lin  JL, Goldberg  R.  Does the Tyndall effect describe the blue hue periodically observed in subdermal hyaluronic acid gel placement?  Ophthal Plast Reconstr Surg. 2014;30(6):524-527.PubMedGoogle ScholarCrossref
5.
Kienle  A, Lilge  L, Vitkin  IA,  et al.  Why do veins appear blue? a new look at an old question.  Appl Opt. 1996;35(7):1151.PubMedGoogle ScholarCrossref
6.
Monnier  P.  Standard definitions of chromatic induction fail to describe induction with S-cone patterned backgrounds.  Vision Res. 2008;48(27):2708-2714.PubMedGoogle ScholarCrossref
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