What i would like to know is what colors i can use for all us army uniforms?

Do a search for World War Two reenactment groups and uniform collectors, and you should get a nice selection of color photos to work from. Uniforms were manufactured in vast numbers by numerous vendors, so colors varied considerably, even before you consider color fading in use. The uniforms were substantially redesigned during the war, as well. Nearly everything was labeled "Olive Drab," but that was a term of convenience, and a whole host of colors fell under that general term.
Broadly speaking, the M1941 uniforms combined brown wool pants and shirt with a tan or light green field jacket (known as the Parsons Jacket, after its designer). The Parsons Jacket, which resembled a windbreaker, fell out of favor because it wasn't warm enough, and many troops bartered or otherwise "acquired" the tanker's jacket, which was similar in cut, but had elasticated cuffs, waist and neck, and was fully lined with blanket material. Shoes were dull, russet leather, and puttees were tan or olive canvas. Web gear belting was tan or greenish. There was also a green cotton, herringbone twill fatigue uniform issued in hot weather conditions.
The M1943 uniform, which became common only late in 1944, was a dull green or greenish-brown color (though very early batches were made in a slightly shiny sateen fabric).
The M1944 version was a brownish green wool uniform with a short jacket (known as the "Ike Jacket," because Eisenhower was an early adopter). Though seen among some rear echelon personnel, it only really became common after the fighting ended.
Metal items, like helmets, were generally painted No. 9 Olive Drab.
As a practical matter, you'll need a selection of ochres, greens and browns, and you'll probably need to do a lot of custom mixing. The mistake young modelers always make is buy one bottle of Olive Drab hobby paint, and use it to paint the tank, the jeep, the helmets and the uniforms, when in real life, they were all different colors. Look at reenactment group photos, and you'll see what I mean.

Incidentally, I assumed that your question was about World War Two uniforms, as that is probably the period of greatest interest among armor modelers. If your interest lies in the Korean War, Vietnam War, Cold War, or the modern period, the answers are more daunting yet, and I suggest you buy the appropriate Osprey books (in their Warrior or Men at Arms series), which include histories, photos and color plates of uniforms from all eras.
Post script: I should have referred to "gaiters" in my previous post, not puttees, which are bands of cloth wound tightly around the lower leg--those were commonly seen in WW1, not WW2. Later in the war, a high top boot became available.

Hi

re the WW2 colours

I found Vallejo US Field Drab quite a good match for the brown pants (trousers) and DOA's US Field Drab quite a good match for the Parsons Jacket.

Its amazing how different the same colour can be from different paint makers.

Paul

The best online resource I have found is:

http://www.usarmymodels.com/guidetopainting.html

LifeColor has a couple of WWII US uniform paint 'sets' that include quite a few of the shades mentioned above.

Where can i buy LifeColor in the usa?

SpureBrothers carries the line, and supposedly just got a new supplier so they'll be able to get it easier.