I have run into problems concerning Atari graphics. I would like to mix more than two graphic modes onto one screen. I don't know how to instruct the computer to create multiple graphic modes nor how to write to a particular mode without affecting the others.
Another problem: how do you instruct the computer to create colors in each individual graphics mode?
There is an article in COMPUTE!'s First Book Of Atari which would be of help to you: "Designing Your Own Atari Graphics Modes." Also, you might want to look at COMPUTE!'s First Book Of Atari Graphics, which was just published (December 1982).