Seeing as how blue eyes are a recessive trait, I was thinking perhaps that other eye colors have come and gone for humans, simply because they weren't passed on to the next generation. If there were humans with alternate colored eyes, perhaps it would have been noted?
Aside from pink/mauve colored eyes in some albinos, unusual colors are not biologically possible. The only kind of pigment your body is capable of producing is melanin, which only come in brown for eyes. People with brown eyes have a high concentration of melanin; while people with blue eyes have a low level of melanin a and light will refract in the eye at similar level as the sky or the ocean (the eye itself is not actually blue just like ocean water is not actually blue, there is no blue pigment in human body). Green and hazel eyes have a tiny bit of melanin, but it's so "diluted" that it appear yellow, it combine with blue eyes and make green.