The book Designing Arcade Graphics by Ari Feldman is available online here (http://wiki.yoyogames.com/index.php/Ari_Feldman%27s_Book_on_Game_Graphics). Even though this covers arcade graphics, it has applications in demo coding since it discusses things like color depth and aspect ratio. Might have some useful info in it.
I took a look through that. For the most part it is pretty good. There are some parts that I really disagree with him on however.
The chapters about colour mixing are very interesting from a first glance.
Maybe it will even help me get a clue about colours.
Just remember it is "impossible to create a good arcade game in 256 color mode". ::)