Speaking of "the hair", what's up with that? Is it a piece they stick on, or do they plaster the actors hair up like that? I suspect a bit of both for the Centauri. At first I thought the hair was silly, but it's grown on me.
There was no description in the script but the theory was originally that the height of the crest would indicate rank. When they were first doing tests, they had the wig swept up and as a joke, Peter Jurasik showed it to JMS and said that he loved it. JMS, trying to be supportive of the actor's choices said to go with it. Then nobody wanted to go to the Executive Producer and confess to the joke so it stayed.
As far as I know it's entirely a wig on Londo and Vir.