Spider-Camouflage: Spider-Man can use Stealth. When it's not your turn, lines of fire can't be drawn to Spider-Man if he's adjacent to blocking terrain.

Will walls activate Spider-Camouflage?
Yes. Walls are blocking terrain. Some effects specify SQUARES of blocking terrain, and walls are not squares and will not work in those cases, but Spider-Camouflage does not mention squares. Walls work just fine.

If Spider-Man is adjacent to the edge of elevated terrain, will Spider-Camouflage activate?
Only if there is some actual blocking terrain also adjacent to Spider-Man. Elevated terrain, by itself, is not blocking terrain.