Asaleth is primarily a feudal age kingdom. I don't have anything specific in mind for them color wise for their banner. Their armor will be a lot of dreary grays and winter colors, something typical of their time and serf and lord lifestyle. Illoriaon, in a large contrast to Asaleth, should be wearing primarily bright silver, white, gold, armors with a very pure look. Feudal banners are known to contrast that with some pretty vibrant colors though, so I dunno. Perhaps Elenmmare can suggest some sort of color scheme.
Blighted Plague items should be black (color of death), white (color of winter and bone), and blue. There may be some occasional red mixed in, but not as much as the Feron.