Iris colour
The colour of the ring around the pupil, set mainly by how much melanin the iris holds.
Also: eye colour
Eye colour comes from the iris. Brown eyes, the most common in the world, have a lot of melanin in the front layer of the iris; blue eyes have little, and their colour comes from how light scatters in the tissue, as with a blue sky. Green and hazel sit in between. Many genes are involved, with OCA2 and HERC2 playing large parts, so eye colour is not inherited as simply as old textbooks said.