a good starting point (in my opinion) is the Combat Patrol (Games-Workshop Homepage). Every unit of this kit is kind of usable in the right setting.
After that it is up to you, whether you wanna play suit-, vehicle- or infantry-heavy. Or maybe a healthy mix out of them.
T'au is all about preference, skill and personal playstyle. A tournment winning list is often doomed to fail in the hands of a beginner ...
Regarding color palettes for T'au septs, please just google that.
I don't know if I can post them here because of copyright reasons.