No, it’s entirely possible to have green-brown eyes. It sounds pretty exciting actually! (My mom has one green & one brown eye. :D)
Oh yeah, I definitely have greenbrown eyes! Green with a bit of brown in the middle. They’re pretty awesome, in my opinion. But I normally just say Green because if I say greenbrown (which isn’t a word, I know), people say, “Oh, you mean hazel?” And I don’t like saying I have hazel eyes because hazel isn’t an eye color, it’s an eye type.