"The Nigerian becomes a Naturalized black South African. Nothing wrong with that right?" Mr. (or Ms.) Merwe, is there a problem with that?. I do not mean to be rude or insensitive to your 'plight' but don't you think it is better to "leave the kitchen if you cannot stand the heat"? 
Apart from original Black South Africans, 'others' were also immigrants (either through force or the legal route) and here we are venting as 'South Africans'!!
Why bring in the issue of race? Whether black or white, should there be any demarcation? But since humanity no longer exist due to selfishness and insensitivity, we use the skin colour as our best defense. 
Please let us embrace unity despite our differences and diversity. It is not about being black or white or an immigrant, it is about humanity....

NB- I am not Black, not White, not a South African, not a Nigerian, not an American. I am a human Being.