The mystery blonde who’s been accused of destroying Chris Brown’s relationship with Rihanna isn’t exactly a threat … because she says she prefers vanilla over chocolate. 22-year-old Keisha Kimball — a waitress at L.A.’s Playhouse nightclub — was photographed holding CB’s hand last Saturday inside the club … and now she’s being blamed for Chris and Rihanna breaking up. But Keisha tells TMZ, “I am always Chris’ waitress. I know him and am friends with his friends. Nothing has ever happened. I just work there. In the photos, he was handing me a bottle to drink out of. Of course people are going to twist it another way. I don’t go for black guys.” Keisha — who says she’s not racist … it’s just a dating preference — adds, “Whatever is going on between Rihanna and Chris Brown is between them. I’m not trying to be a home wrecker.” And get this … Keisha says CB is normally a great tipper, but last weekend he stiffed her … in the gratuity department of course. As for the CB/Rihanna breakup rumors … our sources say they’re true … but it’s nothing out of the ordinary for the on-again-off-again couple. We’re told Brown and Rihanna break up like this on a regular basis — and things go back on track just as quickly as they derail.