Different colors are best for different locations, but I have found that for night/urban environs, the U.S. urban digi works well as well as has a nice look to it.

For the woods straight O.D., or a pattern like the german reversable spring/fall oak leaf pattern from WW2 is best, though the it is harder to find than the modern east german flecktarn (not as good). Tigerstipe is my team pattern but I skirt that requirement wherever possible due to my belief that the pattern is not very effective.

In the snow the modern german snow pattern is great, it's white with dark green pine needle starbursts and works to break up your outline even where trees are not prevalent.

There is something to be said for being recognizable on the field though. A team that regularly acts as shock troops may just want to wear something easy to recognize so they won't get shot by their own guys by moving too far ahead in a quick advance, even if it's just all black or a distinctive marking or jersey. Whe I was at blanding my base defenders had black jerseys with white sleeves, very good for ID at night so that I didn't shoot them all.

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Wow. One case, one kill. What do you want; A cookie?