It's a very interesting yet baffling question. As far as I know, eye colors are dependent upon the amount of pigment (melanin) found in the iris and how it is distributed. Basically speaking, there are brown, blue, green, grey, hazel, black and violet. Each eye color has its own subordinate colors. Take blue for example. There are aquamarine blue, Arctic blue, baby blue, cornflower blue, crystal blue, denim blue, electric blue, forget-me-not blue, gunmetal blue, indigo, laser-beam blue, sapphire, sky blue and steel blue. Other eye colors also have variations of colors. It is really hard to predict exactly how many eye colors there are in human, but I will just go with what I know. Hope to be of help.