I'm also curious about driving dual color matrix. Typically a matrix would have a shared cathode and 2 sets of anodes for the 2 colors, so 24 pins total on the matrix.
I don't think it would be easy to drive bi-colour led using separate MAX7219 chips because of the way they do all the row and column scanning on chip but if your using common anode bi-colour LED's and double up the segment to anode and maintain the separate cathode to digit then it could maybe work but be a right nightmare to program.
