excuse me, rita was rocking the blonde frizzy do from Drakes Over video so yes Rihanna did copy her, on purpose.
When she caught wind that rita was coming out, she switched from brown to Ritas do to make it seem that Rita was copying her.
In simple terms. Its like a famous chick spotting an unfamous chick on the street and jacking her style and rocking it for all to see so that when the unfamous chick gets public it looks as though SHE is the copy cat when its really the opposite.

I wouldnt be shocked if Jay forced rihanna to dye her hair black when he realized what she was trying to do.