It depends on what you mean by
Modern Gear?
Most older US issued gear (ALICE gear) comes in varying shades of green (with the exception of a few small rucks that are radio carriers and are in woodland camo).
Here are some examples of US Rucksacks, duffles, and a sleeping mat.
Large rucksack:
Medium rucksack:
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Small rucksack:
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Woodland Camo small ruck radio carrier:
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Duffle bag:
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Sleeping Mat:
The green on the duffle bags and ruck sack, etc. is more of a medium green, but can vary from dark to very light depending on wear, dirtiness, etc.
The modern (pre ACU) sleeping bag stuff sack should be overall black (straps, buckles, everything):
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Cots should have medium green fabric and aluminum frames.
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Newer gear is all in ACU pattern for the US Army.
ACU Rucksack, body armor, and personal gear:
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Most newer gear for the USMC is in Cayote Brown.
USMC Cayote Brown gear:
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The USMC still uses their digital pattern and old BDU woodland pattern for their rucksacks though.
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You won't really find any exact matches in any paint brand for them. The best bet is to just use some colors that look about the right shades of green for them. No two pieces of gear are exactly the same color anyways.