There is no such thing as blue eye pigment. The only pigment in human eyes is melanin, the same brown pigment that colors skin. Brown eyes have a lot of it. The iris layers absorb most light and reflect brown. Hazel eyes have a moderate amount. Green eyes have a small amount.
Blue eyes have almost none. Without much pigment to absorb light, the iris instead scatters it - and short blue wavelengths get scattered most efficiently. The result is that blue eyes look blue for the same reason the sky looks blue: it’s an optical scattering effect, not actual blue paint.
In fact, geneticists think every blue-eyed person on the planet shares a single common ancestor. A 2008 study traced a mutation that turns down melanin in the iris back to a single person who lived around 6,000–10,000 years ago, probably near the Black Sea. Researchers think that before then, nearly all humans had brown eyes. The mutation spread through populations and gave us the blue, green, and hazel eyes we see today.
