Does Trey count as 'black'?

I am aware that this question might sound dumb and I don't mean to sound racist in any way, so I apologize in advance for any misunderstandings.
I live in a mid-European country where non-Caucasians are very rare in general and if I would see Gregory Kieth (Trey) on the street I wouldn't think twice about him being anything else than white.
In the show, they occasionally refer to him as to a "light-skinned" black guy. In this case, what is the "criteria" for blackness? I guess one of his parents or one of the grandparents is black - but in the latter, would 1/4 of black still count as black?
Again, I don't want to start any racial conflicts. And I am aware that visibility is important. I'm just ignorant in this area and would like to know.