i don't wear make-up either. i had an ex tell me this, and because i'm a dork, at one point, i spent a lot of time in front of the mirror studying the physical make-up of my eyes. (it must have looked like i was being *entirely* too vain.) the iris bit of my eye looks like it's made up of 'crystals' of gold, green, and blue, and there's a darker blue ring around the outside. this is pretty common in eyes described as hazel - a mix of pigmentations.

i'm only guessing, mind, but i think what's going on is that
1) the different color splotches are different 'patches' of cells and
2) the different patches of cells dilate or contract based on hormones/ chemicals released in various moods - similar to the way the pupil reacts not just to light, but also to mood.

but i'm not a biologist, so i have no idea if that's how it actually works. i just know that when i'm calm, my eyes are dominant-green, and sometimes when i'm worked up, my eyes are dominant cloudy/grey blue. a darker shade of blue - but definately blue.

-bs