The question of what to wear on an African safari depends on where exactly you are headed. The golden rule is to wear what feels comfortable. Cotton shirts, T shirts, Jeans and a hat are all ideal clothing for an African Safari.
Boots are great if you will be hiking and visiting game parks. You don’t really need to wear the so called safari wear especially if you are trying to avoid being recognized immediately as a tourist and therefore sold things at ridiculously high prices.
Note: that getting the balance right is important, not enough is not better than more clothes (clothes help you stay cool if worn propperly and in the right layers!)