SKIN AND HAIR COLOR Skin color has been assessed in a number of ways. Broadband
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spectrophotometry allows the sampling of reflectance (strictly speaking remittance)
at a number of wavelengths such that wavelength-dependent curves
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HAIR AND SKIN COLOR 73
can be plotted (66, 103, 122, 123). How to manipulate these readings may not be straightforward, although most authors choose ratios or absolute values of one or more readings (70). Dermatologists have tended to use the tristimulus systems whereby color is represented according to one of a number of CIE indexes such as the L∗a∗b∗ score, where color is defined on three axes, light/dark, red/green, and yellow/blue (103). This color system is easy to manipulate and can be computed from broadband spectrophotometer readings, although there is a tendency to imagine that individual aspects of the index represent distinct biological qualities (e.g., melanin or blood), which may not be the case (15). Simpler instruments based on a
few reference points using laser irradiation have also been used (28, 32). Any such approaches have to take notice of site, age, and sex variation, and changes due to ambient UVR. For instance, there are seasonal changes in virtually all body sites
although they are least for the buttock (72). Second, it is questionable whether differences
in erythema can be separated from those due to melanin because although
distinct, the spectra overlap (66).
Hair color too can be assessed colorimetrically, as described above. Added
pigments (hair dyes) will invalidate readings. Hair color charts have also been
used but have obvious drawbacks in that ambient lighting is not controlled for, and
they are subjective (31). The hair samples used are usually not natural, and match some populations better than others. As for skin, seasonal variation, although in this case due to bleaching caused by sunlight, is also a confounder.
31. Flanagan N, Healy E, Ray A, Philips S,
Todd C, et al. 2000. Pleiotropic effects
of the melanocortin 1 receptor (MC1R)
gene on human pigmentation. Hum. Mol.