I like the 5.11 Tactical Pants and shirts (
http://www.511tactical.com/511-tactical-pants-mens-cotton.html ). Very well made stuff, lots of pockets and lots of color combinations. The coyote, OD green and tundra are good colors for African safari. Stay away from the khaki color as it is a bit too light. As far as boots for a safari, I've tried a bunch and one of my favorite is the Irish Setter Soft Paw. About $150 from Cabelas or you can go by a Red Wing boot store and they can fit you with a pair. Very comfortable, right out of the box.
Totally agree with the comments from eveyone on not bringing a lot of clothes. Your travel clothes and 2 or 3 other sets max. Daily laundry service is the norm.