You give Tamru some cursory details about Flynn: his sharp (but soggy) clothing, his overappeasing mannerisms, his clear affection for Tephra. When you're done, Tamru asks, "So, what color was he?" He points to his own dark brown skin. "You know, like how I'm black. Was he dark like me? Or lighter? Did he look white? Maybe another race?" He gestures to you with semi-ironic levity. "I know he wasn't blue."
You think about it: he was lighter, pinker. Definitely "white." It didn't really seem significant, down here, but then again, how can you assume that? Even at their best, humans have always had tendencies toward ugly behavior. Maybe human racism has gotten worse since Tamru came down here, or maybe it's stayed the same. You didn't ask Flynn about his society's progress or about his own personal views. You just sort of assumed that he would be accepting. But why did you assume that? Because he fell for a mermaid? Or because you didn't even stop to think about it? At any rate, now that he's down here, he'll have to play nice, right?
Tamru nods his head knowingly at your lack of a response. "So he's white. How's he going to treat me, a black person?"