Hello,
here is my color guide, referencing the Vallejo Model Color line of paonts. I think there are conversion charts on the web if you use other paints.
ACU (ATC pattern)
Base Light Khaki
Pixels Light Grey Green
Pixels Dark Drab Green
Desert MARPAT:
Webbing Iraqi Sand #819
Boots Desert Yellow #977
Goggles Desert Yellow #977
Vest (Coyote Brown) Desert Yellow #977 (Sand Brown #876)
Base Dark Sand #847
Color 1 Khaki #988
Color 2 German Camo Pale Brown #825
Color 3 German Camo Medium Brown #826
Drybrush Iraqi Sand #819
I recommend this article concerning painting German Flecktarn camo at 28mm, the colors are different of course but the ACU/ATC pattern follows the same principles (you won't be able to see if the pixels are round or square at this scale
http://www.dhc-wargames.de/index.php?id=81&L=1The camo pattern that is currently being phased in and which is the norm for Army soldiers in combat zones is based on Crye's Multicam pattern which in turn is used by modern British forces. I have no painting guide for that, unfortunately.