What colour should i paint my American sherman crew? Some pitcures have them as light brown, some light/dark green, other black, i am complerty stuck!

That depends on what jacket (if any) they are wearing. The best reference is your kit box, as this will show you which colour to paint which figure etc. try http://www.usarmymodels.com/guidetopainting.html this link and see what you can come up with. I think that their shirts were that off looking green and then the field jackets were creamy dark yellow, or the tankers had leather jackets. This link suggests that the 1941 jacket was worn on tankers most commonly and it is the dark yellow colour. Dragon 1/6 figs are decent references.

and a little re enactors pic showing both types.

THANKS

Morsecode 1,
ColtM4 covered it pretty darn well, but if I may add one thing; remember that Americans had replacement pools during WWII. This meant that when a guy was with his unit and got injured, he was patched up (if possible) and sent back out to the first available unit (sometimes with a new uniform issue.) So you could have a crew (or any unit) with varying degrees of faded uniforms. So, this means that you can shade the uniforms differently which adds to the drama of the scene. Hope it helps
Ciao for now
Rob