Normally the purple coat is associated with a more benign Londo from
earlier; the dark coat marks a later time.
Who's my alter-ego on the show? All of them, to one extent or
another. They're pieces I've kind of sliced off and deposited into one
part of the story or another. The theory is that, once sliced away, they
are the free to go off and grow into something larger on their own, and
hopefully become something greater than the source.