THere is no such color as “green” in mammals. Human “green” eye color is actually a mixture of brown and blue. If you look very closely at a green human eye, you will see light brown patches or specs intermingled with blue patches or specs.
“green” results when the blue outnumbers or overpowers the brown. Hazel results when the brown outnumbers the blue. Blue-green is when the brown is almost non-existant.
I don’t know what the technical explanation is for grey or steel blue eyes...or the rust brown/red eye color that is common in redheads. THe red color is most interesting to me because it seems to be exactly the same shade of rust-brown as the freckles on the face of some natural redheads.
Sometimes the percieved eye color changes with the change in intensity of light. I once knew a mediteranean guy that had dark brown eyes indoors, but in direct bright sunlight his eyes changed to a brilliant true baby blue. It was freaky.
I once knew a girl ( a truly beautiful natural blonde) whose eyes were partly blue and partly brown, not mixed but half one color and half the other. Actually it was two thirds blue and one third brown. I took quite a few pictures of her and her eyes really were striking.
She told me her eyes were not as uncommon as one would think as she had run into several others with the same type of eyes.
Thats not quite true, as far as I have been taught. Humans are in fact coded with the ability to produce green, which isnt a variation of blue and brown. Now Hazel can be a variation of blue and brown or brown and green. Its all on how your pigmentation, density and melanin are coded.
Now any color that isnt blue,green or brown are either a mixture of those or a true genetic mutation.