Human eye

eye colour, heritable phenotypic (observable) trait determined by pigmentation and light scattering in the iris of the eye. The iris, the coloured part of the eye, is the ring of muscle and collagen fibres around the central black opening of the eye known as the pupil, through which light passes. The colour of the iris is commonly described by simple terms, such as blue, gray, green, hazel, or brown. However, eye colour varies across a continuous spectrum, such that formal classification schemes for eye colour range from simple three-colour systems to considering multiple colours within one eye. Eye colour is also affected by the variable light available in the environment, resulting in different perceptions of an individual’s eye colour.