Image Analysis Tools to Quantify Visual Properties of Hair Fiber Assemblies 302 yellow/red tones. Eumelanin provides black and brown hair with its characteristic color spectrum while pheomelanin is believed to strongly influence the color gamut observed in red hair. Other chromophores in hair consist of amino acids, such as tryptophan, tyrosine, phenylanine, and cystine. Also present are various metabolic/oxidation products of tryptophan, collectively known as the kynurenines (N-formylkynurenine, kynurenine, and hydroxy- kynurenine). While the amino acids absorb in the UVB region of the electromagnetic spectrum and do not provide the hair with any visible coloration, the kynurenines absorb in the UVA region and fluoresce in the visible region resulting in yellowish coloration, which is especially common in gray hair. Synthetic hair dyes absorb visible radiation and produce an array of colors in hair. They are very sensitive to light and shampooing, resulting in a great deal of effort in the personal care industry to prevent color fading, or maintain colorfastness. Hair Luster Gloss: The attribute of hair luster is a significant concern to the hair consumer as well as marketers of finished hair preparations.7 According to the Oxford English Dictionary, luster can be described as:8 1. A gentle sheen or soft glow, especially that of a partly reflective surface. 2. A thin coating containing unoxidized metal that gives an iridescent glaze to ceramics. 3. A fabric or yarn with a sheen or gloss. 4. A prismatic glass pendant on a chandelier or other ornament. Luster is often interchangeably described as gloss or shine. It appears that there is little difference between these terms in the scientific or lay literature. In fact, luster falls within the category gloss. Other gloss classifications include specular gloss, sheen, contrast gloss (luster), absence-of-boom gloss, distinctness-of- image gloss, and surface-uniformity gloss.9 Specular gloss refers to