I attended PG County schools my entire life and was in the minority, in high school. You may not believe this but, I never realized how much in the "minority" I was until I looked at my 20 year reunion class picture. I have my year book too and now looking at it with my DH I do realize there were a lot of blacks in my class/school. While attending school I never realized it, honestly! Although I considered myself a little socially awkward in high school I had friends, mostly black, but good friends some of which I still see today. I think this made me the person I am today. I also came to this country as an immigrant and had ESOL classes, so maybe that gives me a bit of different perspective than others have, I know what it's like to be different, although I'm white, but I can relate to having to be accepted.
Today, my kids attend FCPS; the elementary school they attend is considered "diverse" by many, the principal mentioned it on back to school night, which I thought was a bit strange. I never take notice of how many whites there are or blacks, hispanic, asians, etc. are in attendance at school functions, while some of my neighbors do take notice and comment on it. "Did you see how many Indian kids are in Johnny's class" ...... to me people are people it doesn't matter what their skin color is.
OP, I think your child will only notice if there's a "big" deal made of it. Of course someone is bound to say something about color and that's when he will probably realize it. I think it makes kids more accepting of society to be around different races/cultures, there's always an opportunity to learn something new about a person no matter what color their skin. I'll never forget when I was in the doctor's office years ago with one of my boys and a little black boy came up to one of my boys and say "why is he so white" I just laughed because it was funny and it's true my kids are very white. His mother was mortified!