I know chameleon stopped existing since Oblivion, either due to time constraints, or because the devs thought they couldn't balance it or other unknown reasons. Anyways I've been wanting to make some NPCs partially transparent so it would be harder for the player to see them, the point is they are supposed to be extra sneaky humanoid npcs. One way to do this it seemed, was to add a ghost effect to the NPCs, but the problem is it adds this glowing blue aura which I'm not sure makes them harder to see. Further more, these NPCs are not intended to be identical to ghosts, they are intended to be magical/stealthy NPCs with high illusion skill.

What exactly would be the easiest way of going about this? If this is a task of unrealistic difficulty, is there some sort of combat style, or script, that will make an NPC cast invisibility, and use hit and run tactics?

Nevermind I learned how: The key is to make a duplicate ID of the dead version of the ghost effect, and alter it to the enchant/spell effect ghost effect version to the dead ghost effect version, and then it's much harder to see the NPC.

I've never tried doing anything like this in Skyrim, but I immediately think of the actor's alpha value.

Have you tried http://www.creationkit.com/SetAlpha_-_Actor?

What's the dead version of the ghost effect called? Does this effect head tracking?

I was thinking about making a chameleon spell as well for my illusion spell pack since the invisibility spell acts strangly when the npc sees you cast it.