What is the best explanation for the many shades in human eye color?

Eye color is a polygenic phenotypic character and is determined by the amount and type of pigments in the eye's iris. The genetics of eye color are complicated, and color is determined by multiple genes.

In human eyes, these variations in color are attributed to varying ratiOS of eumelanin produced by melanocytes in the iris. Eye color is an inherited trait influenced by more than one gene. These genes are being sought using associations to small changes in the genes themselves and in neighboring genes