I can see it as a nn (
Graham?). I don't like it, but I can see it.
I cannot see it as a fn for either gender. Of all the names / ideas / places in the world, someone wants a gray child? Perhaps I'm being petulant because I got my first gray hair when I was 12. But still, I can't see this as a real name for either gender.
Now, subtle allusions to grayness in names, like
Griselda, don't bother me at all. In fact, I'm rather drawn to the name
Griselda. But in-your-face
Gray? No thanks.