Valmur_Dwur
First Post
Ok, lets break this down:
Astral-appear normal although you can see their silver cord
IMC: appear silvery per MoP
Ethereal-appear translucent per hong's OA reference
IMC: same
Invisible-appear normal
IMC: this is where it gets tricky
the DM (that's me) has too take into consideration several things. How the person who is invisible is acting and how the pc who sees this person sees those around the invisible person is acting. So you need to figure how the person who is invisible is acting ie: Does he look like he's sneaking around? Does he stop and interact with other people? Then you need to do the same with the pc. Either give them a roll for spot or another skill like scry, search etc. or RP it out by telling the pc verbally or with a note what he perceives to be going on. This is fun if you plant a couple of decoys to mimic some things that someone who is invisible might do 
Astral-appear normal although you can see their silver cord
IMC: appear silvery per MoP
Ethereal-appear translucent per hong's OA reference
IMC: same
Invisible-appear normal
IMC: this is where it gets tricky

