Like Ogri stated, but it is not just the actual fabric of the clothing that makes you blend in...Shape, shine, shadow, shimmer, spacing, smell, silhouette and movement all need to be taken into consideration.
You don't see a sniper in just his camo-suit he also wears a ghillie suit, into which he adds local materials to blend in with his surroundings...
We used to do a test when cadets, to see how close a team could get to an individual before they could see him, and the clever bit was when the individual had to say what the others were doing...It is not just the case that they cannot see you...you must be able to see everything that is around you...
You need to be a chameleon
LS