your grave/bed problem is something you might not be able to fix with pixel manipulation. I think that you would necessarily need some symbol, a tombstone or whatever, to convey that somebody is buried there. Mounds of dirt, even in real life, don't necessarily give off a grave vibe, not even the ones that actually are graves. In the event that the corpse scrambles out to attack you, it becomes clear, and I mention this only because you mentioned that this is for a shooter, so I figure that it might happen - but before that point, the player probably won't be sure of what they're looking at.