You don't need to be smartly dressed on safari. The most important thing is to be comfortably and practically dressed. On safari, the colors green, khaki, brown or grey are really useful, because white, red and other bright colors might scare away the wildlife. Some ladies may want to consider packing a sports bra as many of the roads are quite bumpy.
Open sandals or other comfortable shoes may be useful to wear in the car when it is hot. Please bring some warm clothes! It gets really cold in some places because of the high altitude, especially in June, July and August.
Of course it can also get very hot! It is probably best if you dress in layers, that way you won't be chilly in the morning or evenings and as the day gets hotter, you can just take off your layers and stay cool in the lighter clothes you're wearing beneath.