I personally think that if you're not planning specifically for it, then it just happens. It's a reflection of your shopping habits: REI versus Army/Navy stores vs. Hunters-R-Us down the road.

If you're like me, you grab bargains when you can and frequent a bunch of outdoor-oriented places. So while I have a blue Kelty backpack, I also have a coyote-colored BOB. My sleeping bag is bright blue from TNF, but I have a camo bivy bag. Most of my pants are khaki or OD, but tops are reds and blues. I do intentionally have a few blaze-orange items (hat, bandana), but mainly this was b/c I used to day hike in places that allowed hunting.

I think it just happened cuz something was on sale, or had features I liked. I suppose I could seperate stuff by "seen or not" but really, I just use what I feel most functional, at a rational price.