While in any sort of natural terrain, you can use the Hide skill even while being observed.
Prerequisites: 17 ranks in Hide and Survival
Classes: Ranger (17th), Scout (14th)
Prestige Classes: Nightsong Infiltrator (10th), Shadowspy (9th)
Related to, but does not require camouflage.
Limited to natural terrain (nightsong infiltrator, ranger, scout), or sunlit natural terrain (shadowspy). Not limited for urban ranger.