Ok, after struggling with the SPI a bit (I still have not managed to transfer more than 4096 bytes/transfer) I decided to code around the problem for now.
I implemented a color handler that builds a color table of all sprite shapes and bitmaps needed for a specific “scene”. This seems to work well.
So, tonight, for the first time, I loaded a BMP file with 320×240 pixels and about 80 used colors. Tadaaa! 🙂
I then loaded a few test sprites which added a few colors more and placed one on a higher layer. And that worked perfectly too, both concerning colors and everything else.
Happiness! 🙂