Rape is unwanted sexual contact from a individual/group with a higher level of privilege than the party being assaulted. I.e., sexual contact + power. Since the system is structured to provide men with more power than women, regardless if a woman's sexual advances are unwanted, they have less systemic power then men, and thus cannot commit rape.
Similarly, just as minorities cannot be racist towards white people, since racism is defined as a combination of "power + privileged," minorities cannot rape white women. Minorities fundamentally are less empowered, and thus cannot commit rape against white people, regardless of whether or not they consent to their sexual contact.