The previous piece by adamk is not only academic to the point of pedantry, but detached from the diversity of the reality its title invokes. This is a pity as the subject matter is intrinsically interesting - at least to some.
Without pretending to make good the abovementioned deficiencies, let me give an example of complexity seemingly invisible from the ivory tower: there has always been an element of resistance to hegemonically defined white identity, (not only in South Africa, but in other settler societies), which was highly repressed by dominant settler groups.
The term "going native" throughout the British empire (including South Africa) marked a discourse of derogation of "whites" who deviated from assigned racial roles. The term "kaffirboetie" (literally, "heathen-brother") carried massive stigma in dominant Afrikaans speech.
Stigmatisation, however, was the gentlest tool of control. The Dutch "vogelvrij" was a legal status assigned to whites who went native; meaning bird-free, it stripped its targets of protection; they could be shot as freely as birds. The Afrikaans version, Voelvry, was the title of a multi-band tour of ("white") anti-apartheid musicians in the 1980s - well before adamk describes whites reconsidering received identities.
One of the best-kept secrets of South African society is how many "black" families contain one or more "white" ancestors - "best-kept" because it undermines the now-hegemonic Africanist nationalism just as it did the previous hegemony.
Not only did going native offer an escape from repressive settler culture, but also a special status within the adoptive community, as mediator between indigenous and incoming cultures.
The Zulu king Shaka elevated certain white men to the status of chief; since political networking with other chiefs required taking wives from those chiefs' clans; hence large numbers of descendants.