The display board takes one out of every 4 pixels from the StrongARM (in STN LCD mode) and drives this to the VFD with some manipulation - see the linux kernel display driver source for more info.

The StrongARM will support 16-bit TFTs (see the Visteon Camelot for an example) however the top 16-bits of display info come from 8 GPIO lines which are most definitely in use on the carplayer - hence, it's not possible to bodge this in very easily.

OTOH, in theory you might be able to put the LCD controller into 16-bit mode, but use only the lower 8 bits of display info. This is available, along with the frame/line/pixel sync info, on a connector pad-out just above the CPU on all mk2/mk2a players.

This could give you some sort of colour, though it may only be of limited usefulness and would require hacking of the kernel display driver so that the player output to (at least a part of) the actual LCD display.

Hugo