Apartheid was theoretically a multi-state solution. An obvious problem is that the vast majority of the black population lived outside of the states that were set up. In reality, the purpose was to deprive them of South African citizenship and rights, by instead claiming that they were really citizens of some other country. So, no other nation besides South Africa ever recognized these "countries".

As for a two-state solution, that was never seriously discussed. The white population is a majority in few areas, any white state would have to be a multitude of non-contiguous tiny splotches utterly surrounded by the other state. A white/coloured state would have a much more substantial eastern base, but there would still be a multitude of non-contiguous tiny enclaves in the east. And coloured people where never accorded full civil rights by the whites anyway, so there's really not much basis for a union of them.

A comparison between the policies of Israel since 1967 and apartheid is sometimes made - the accusation, I suppose, being that a west bank that has seemingly been under permanent Israeli occupation puts the people of the west bank under an apartheid like situation, citizens of a theoretical state that actually has no sovereignty. But there is a long standing basis for a division of the area between arab and Jewish states, this didn't exist in the South African situation, so no two state solution would've made sense there. The situation is further differentiated by the fact that Israeli Arabs actually living in Israel have full civil rights.