Strange can't help but give Beau a little frown as she calls him out. He would appreciate it if she didn't do that! Come on, Beau, cut him some slack!

"I don't know what a tiefling is," Strange admits, like the fact that he had to admit not knowing someone is the end of the world. "But how many blue or purple colored people could there be?"

That's what she meant by blue, right? A blue person? Strange, who's dealt with people who were furry, scaled, or feathery, is at least assuming that's what Beau means by blue and purple.