@enthusi : a few years ago I searched for a description of C64 “unofficial” graphic modes, those that exploit some hardware features to provide more colors or better resolution or less restrictions. I found the following page, that explains some of them:
http://www.studiostyle.sk/dmagic/gallery/gfxmodes.htm
It is my understanding that these modes are mostly used in demoscene productions, but would it be possible to use them in a game as well? Are there C64 games that use them?