A study of wool pigmentation showed that coloration in hair fibers is produced by either eumelanin or phaeomelanin pigment granules. The former granules are responsible for brown/black hair color whereas the latter produce tan colored hair. Identifying fleece color involves counting the percentage of pigmented fibers. Handicraft workers' demand for naturally colored wool has increased the interest in breeding sheep to produce a desired coloration. Until recently, pigmentation had largely been determined by the naked eye's nonstandardized evaluation of fleece color. Research in color genetics helped to establish color scales to define and standardize shade. The molecular structure of melanins and the colors produced by them were studied using electron spin resonance.