This is an interesting topic. I just watched "the men who stare at goats", and they made a passing reference to "invisibility", which I found amusing.
I think its 100% correct that camoflauge matched to your environment is the most effective. Yes, a while panel van with a generic label on the side may stick out in suburbia-but, in a large city, it blends right in. Cars that blend in almost anywhere are the 4-door grey nondescript sedans. Clothing to match your environment. And, believe it or not, your mindset.
I geocache on a fairly regular basis, and part of the fun of the game is not getting found out. Sometimes, this can get a little creative. I had read stories of people walking around with clipboards, looking authoritative, with a reflective vest on-and were never questioned. Its not so much they are blending in, but that people percieve them as someone who is there for a reason-and usually isnt questioned. They are practicing deception moreso than hiding in plain sight-and it is VERY effective.