I mean, if you think about it, it's clear that eye color is more complex than "brown dominant, blue recessive." Look at all the variation out there! And we've known for a while that there are several physiological factors in play: a couple layers of tissue, varying distributions of melanocytes creating various amounts of two types of pigment in the outer layer, and structural color from Tyndall scattering having a greater effect with less pigmentation.

And now science has newly identified an additional 50 genes that contribute to the pigmentation and structure of the iris:

• The press release
• The study

I really recommend looking at the study if this stuff interests you. The abstract, introduction, and discussion are mostly lay-readable.

Now, mind you, this doesn't mean it's open season on giving your characters "unique" eye colors because they may, technically, not be completely impossible. The most common colors are still the most common colors, the documented patterns of heritability are still the documented patterns of heritability, and a superficial trait like eye color is still no substitute for good characterization when it comes to crafting a memorable protagonist.

But it's fun to know these things, isn't it? ^_^

~Neshomeh