An fire elemental is standing in a large body of fire?
An water elemental is swimming in a large body of water?
An air elemental floating in midair?
If you can see through the medium, then I think you should be able to see the creature.
An earth elemental is underground?
If you mean using Earth Glide, then "Its burrowing leaves behind no tunnel or hole, nor does it create any ripple or other sign of its presence." If you mean just standing in an underground cavern, then if you can see it, you can see it.
Not for nothing, but everything gains total cover submerged in water as seen from the land.
Attacks from Land: Characters swimming, floating, or treading water on the surface, or wading in water at least chest deep, have improved cover (+8 bonus to AC, +4 bonus on Reflex saves) from opponents on land.....A completely submerged creature has total cover against opponents on land ...
Personally I find that rule bogus, there are spear fishermen after all, but there it is.
Smoke provides concealment, and DMs implicitly get some latitude on what else does, and staring right into a bright light does interfere with vision, but rules don't say fire itself does.
Real question seems to be do elementals get a bonus to stealth when in their element. Seems like they should (camouflage and all). All but the fire elementals do get a trained stealth skill, which could represent that natural camo. Assumption for fire element could be they're not usually encountered in a fire, as opposed to air in air, water in water, earth on earth. I'd definitely give a fire elemental a 'terrible conditions' circumstance bonus against observers perception (see perception), if the thing was hiding in a bonfire.
Real question seems to be do elementals get a bonus to stealth when in their element. Seems like they should (camouflage and all). All but the fire elementals do get a trained stealth skill, which could represent that natural camo. Assumption for fire element could be they're not usually encountered in a fire, as opposed to air in air, water in water, earth on earth. I'd definitely give a fire elemental a 'terrible conditions' circumstance bonus against observers perception (see perception), if the thing was hiding in a bonfire.
Well put. People ask a lot of these questions without realizing that modifiers are purposely left vague. General rule is, if you think that a situation should affect a check, apply a modifier. The skill description often have a good deal of vague modifiers as well as the more specific ones.