There are mixed reactions to the way Glee is handling the storylines about race. I believe the people who say that just because the characters feel a certain way, that doesn't mean the writers feel that way. There's quite a lot of talk about whether Blaine is a white character. At least a few bloggers make the point that many viewers just assumed he's white because he has light skin. I was in the "assuming" category, for whatever that says about me. Rachel did make that comment about how Blaine could give her "vaguely Eurasian-looking children."
I have in the last few weeks learned different words for this, "pinoy" being Filipino and "hapa" being a Hawaiian word for mixed. I think it would be interesting if Blaine was a person of color. I don't have a strong personal investment in this, but I'd love to see the explanation for why Mike and Tina hadn't commented on it. The actor who's been cast to play Blaine's brother is white, so we'll see in April or so if he's a half-brother. I definitely want to see more of Blaine's family dynamics.
Glee is doing long storylines around race, disability and sexual orientation in season three. They've done so before, but it seems to be pretty political this year. Blaine is openly gay. I would think he'd be equally open about being racially mixed, if that was the case for the character.
[As of January 2014: Still nothing totally definite, but after what I've learned and various other in-canon hints, I go with the "assuming that Blaine is multiracial until told otherwise" viewpoint.]