The possible eye colors of human beings are amber, blue, brown, gray, green, hazel, and in the case of complete albinism, red based on the Martin-Schultz scale of eye color. In general, eye's iris pigmentation and light scattering frequency determine and change the eye colors. Various eye colors can occur in different parent-child combinations due to the complex eye color genetics. Violet is not mentioned in the category, while such colors may be a sign to indicate the pathological changes, like albinism etc, which is also said by the albinism.org. I think perhaps "violet" eyes was just categorized as blue because that is what they actually look like.