You will have to read up on the standard accepted in S. Africa to find out why. Different countries allow differences in breeds. In my breed, Labs, a certain controversial colour is described quite differently in the U.S. AKC than it is in the Canadian CKC. And I do not mean to mislead you as it is not the registering body who devises the standard but rather the breed club. You need to find the breed club for S. Africa. Sometimes though, the registering body is easier to find.
Out of curiosity I did check here http://www.staffordcanada.com/canadian.html
You can see the colour is not encouraged but it is not listed as a disqualifying fault. It doesn't say why. In Canada that is. We don't have many Staffies here. I've only seen one real live one and I was amazed how small they are. Think in my mind I'd confused them with the American Staffy up till now, which are bigger.