How do eyes get their pigment?
The iris (the coloured parts), as with most body parts, consists of multiple thin layers. The rearmost two layers of cells produce a pigment, called melanin. Melanin is the pigment also produced when you tan, causing your body to darken, or in freckles. As such, brown is the most common colour of eyes. However, obviously not all eyes are brown, as melanin appears. This is because other components scatter the incoming light, causing some wavelengths (especially the shorter ones) to not be seen. This is similar to why the sky is blue during the daytime. Furthermore, collagen, a fibrous substance made from long, thin chains, acts as connective tissue in our bodies. Varying amounts and composition of collagen also produces variety in the wavelengths of light that are absorbed, as does haemoglobin in the blood vessels within the eye, adding to the variety of colours than can be seen.
