The resolution is standart 320x256 I think? And I would agree with khph_re - you could let people send their backgrounds of given parameters so you can choose the most suitable ones. I think it is a good idea to have graphics from more authors.
Originally Posted by fishyfish
The only "absolute" in regards to any given level is that colors16-31 are used for sprites, so those particular colors are set in stone (which in effect also means 48-63 for ehb levels).
So if we are talking about 64 colors game, I think color 0 shouldn't be used for graphics (as it is mostly used for fonts etc), and we have colors 1-15 adjustable for graphics (and 48-63 of ehb variants). Sprite colors 16-31 would be fixed for the whole game?