I painted my Chaos Warriors WHFB army about two years ago. It was my first fully painted army, too. Thus, my skills have improved, so I am going back and updating the army for the new book.
I wanted the warriors to look like they where glowing suits of armor. The BSB (Skull guy) is the skull collector for my Sorcerer, so he can analyze the brains of enemy mages. My fluff is that the Sorcerer sacrificed his warband to gain power ala the manga, Berserk.
I am repainting what was my Khorne Warriors into Nurgle ones. The Tzeentch warriors are the souls of the warriors, where the Nurgle ones are the bodies. I am painting the skulls' eyes glowing blue to show that they are powered by Tzeentchian magic.