I think we talked about this a little bit when they first announced the cast. I'm oblivious, but I had no idea Rue was black when I first read the books. I think it's because Katniss is constantly comparing her to Prim, so in my head she was Prim with dark hair.
That being said, I wasn't filled with rage when I saw who they cast for her role. I just questioned my own reading comprehension.