timmaah, I would think using a normal C two-dimensional array would be better for you than to do this yourself.
unsigned long displayBitmap[2*32][2];
It's much more convenient to say displayBitmap[location] than it is to remember displayBitmap[location*2+color] or accidentally get it wrong when you change the number of possible colors. Let the compiler do the addressing math, it might also be able to optimize better than you can.