When asking about somebody´s eyes? Would you go for " eye colour" or "colour eye". Then if the latter were the more frequently used how would you parapharse it. The former would be "the colour of his-her eyes".In addition, would you use the same structure to refer to hair eg: hair-colour or colour hair.
When asking about somebody´s eyes?
What is the color of her eyes?
What color eyes does she have?
What color are her eyes?
What is her eye-color?
All are grammatical, but the last is the least natural; it is how the question might be phrased when someone is filling out a bureaucratic form, like a police robbery report.
If a guy is telling his friend that he has met a nice girl who he thinks is pretty, his friend won't ask him "What is her eye-color?". No, he would ask "What color are her eyes?"
Typically, it would be "eye color" or "hair color"; that is, the thing which is colored is initial.
English tends to be "head-initial" meaning the head of a phrase precedes complements (https://en.wikipedia.org/wiki/Head-directionality_parameter). So something meaning "X of Y" is typically "Y X".
I hear birdsong
is equivalent to
I hear the song of birds
I hear songbirds
I hear birds which sing