I have a couple of unofficial rules when it comes to painting up these mini Joes.
1) I won't reuse that same miniature for different characters (at least in the same toy line.)
2) If a character gets a totally new costume, I'll use a different mini for it.
3) If a character has an alternate look that's just a repaint of the original (for example, Tan Grunt), I'll use the same mini.
Of course, there are exceptions to these rules.
Anyways, here's Tan Grunt:
I wasn't originally going to do alternate costumes, but after doing original Hawk (and since I had the extra Zerboz Military lying around) I went ahead and did it.
If I start to run out of Joes to paint (hah!), I may delve into the repaint teams like Tiger Force and Slaughter's Marauders, but I'd probably hit the odd foreign characters first.