Technically you aren't supposed to wear partial (or complete) uniforms which you are not entitled to wear (including active duty wearing another service's uniform).
But plain camo has been out for so long, in so many iterations and color combinations and patterns, sold by military clothing sales and civilian outfitters, that it really is not problem (with all insignia removed).
The US military itself is constantly changing camo patterns, though I would not personally wear a camo pattern that was
currently worn by a service branch that was completely distinctive from all other camo patterns (and I think most of these are
sandbox colors as opposed to woodland colors).
I have some original (USAF clothing sales)
woodland BDU military shirts and pants (summer rip-stop and winter poly mix) and an OD fatigue jacket, with insignia removed that I am no longer authorized to wear, but I'd wear them if I felt like it. (but not like to Arlington Cemetery... more like for yard work)
Back in my day, we had certain overseas SP cops who wore Tiger Stripes, but weren't allowed to wear them back in the states. But the military is full of regulations regarding proper uniforms.
I once told a female captain she was required to wear a (OD/black/white) Tshirt under her woodland fatigues (her prodigious lacy brassiere was showing). She didn't believe me, and I pulled out the reg to prove it. I didn't mind seeing her underwear at all, but the general down the hall might have given her sh!t for it. She had recently transferred in from the Navy and didn't know any better.

Finally, you will see numbers of military veterans (of all wars) wearing partial or complete uniforms in parades, or PGR missions, or reunions and the like, and although it is against the rules, no one should ever complain; they are honoring their past service and sacrifice. At
Rolling Thunder in the Pentagon, I wore my woodland BDU cap with captains bars. But wanabees piss me off.