Green eyes are not green
Roughly 2% of people have green eyes — and not a single one of them has any green pigment in their iris.
Green eyes are the rarest of the common eye colors. About 2% of people worldwide have them, and they cluster heavily in Northern and Central Europe — Ireland, Scotland, Iceland, parts of the Nordics. If you go looking for them in most of the world, you won't find many.
So why are they rare?
Eye color is controlled by a handful of genes (OCA2 and HERC2 are the big ones, with several modifiers), and the specific combination that produces green is uncommon. You need low-to-moderate melanin in the front of the iris — less than brown eyes, more than blue — plus the right modifiers. Brown is dominant and ancient, blue is a well-known mutation that spread widely, and green sits in a narrower genetic sweet spot.
Why are they green, then?
Here's the strange part: there is no green pigment in the human eye. None. The only pigment in any iris is melanin, which is brown. What you're seeing as "green" is a trick of physics.
The iris has two layers. The back layer holds dark melanin. The front layer scatters light. When light enters an iris with very little melanin in the front, the shorter wavelengths (blue) scatter back out — that's Rayleigh scattering, the same effect that makes the sky blue. Add a small amount of yellowish melanin in the front layer, and the scattered blue mixes with that warm tone. Blue plus yellow equals green.
So green eyes are blue scattering plus a hint of brown pigment. Take the melanin away entirely and you get blue. Add more and you get hazel, then brown. Green is a very specific in-between.
Which means…
If you shine the right light through a green eye, or look at it from the wrong angle, the green can shift toward gray, hazel, or amber. The color isn't fixed in the tissue — it's an optical effect happening in real time, every time someone looks at you.
Here's a short video that covers it well: youtube.com/shorts/yI-eEN6S1VA