South Africa's current flag, besides for being unique in that it has 6 colours (in the main design), carries a fair amount of symbolism - surprisingly more than one may realise. Visit the Southern African Vexillological Association's site for an interesting overview on the meaning behind each colour and the general flag design.
If you're very into flags, then also take a look at this poster (which it looks like the vexillological association sells for a small fee). It gives a fairly comprehensive view on the various flags flown over our country in our colourful past.
In case you're wondering, the Afrikaans sentence "Vanaf die geboorte van 'n nasie tot 'n onafhanglike republiek" means "From the birth of a nation to an independent republic" in English.