Why is Athena "gray eyed"? Obviously because her eyes are that color, but I suspect there are deeper, symbolic reasons for that particular color and description. This is in regard to the epithet γλαυκῶπις, in the lexicon defined as "bright eyed", but which is often translated as "gray eyed" by poets.

The word γλαυκῶπις shares its root with γλαύξ, the word for owl.

Owls are known for their large and distinctive eyes, which are adapted for low light hunting. Thus, I believe the epithet is a comment on Athena's perceptiveness, telling us that the goddess of wisdom can see even through the dark.

You may find more information on Athena's association with owls in Wikipedia.