These two sound — and look — similar because they have something (or someone) in common: Prince. He discovered them. He produced and wrote their music. And he compensated for their lack of singing abilities by sexing up their voices. In fact, he conceptualized Apollonia's music career (and cast her in the film Purple Rain) following his breakup with Vanity.
(Photos from left: Ron Wolfson /Landov, Andy Kropa/Getty Images)