Negroes, mulattoes like to spank white girls in all holes. The fact that this brunette is also a charming girl - gives a glamour to what is going on. And he's just using her as a device to jerk off his dick and lick his balls. He uses it and then he flushes it. And she's satisfied.
Four went, and two came for more, for they understood, what they face in the end, and they wanted a hard fuck, in fact, that's exactly what they got when they undressed and put their holes under development.