I love MESS's LCD simulation. I forget, can they optionally output black on white? Do all handhelds that have LCDs have the simulation available?
It's just a matter of enforcing square pixels (there's a layout for this) and chose two colors that mimic as closely as possible the original colors of the LCD - the HP48 drivers go in a lengthier effort to emulate the 16 shades of their peculiar display.
The CoCo3 driver implements the layout concept to emulate the palette switch that occurs when the machine is connected to a RGB or a Composite monitor - maybe something similar could be done in order to switch between B&W, W&B and photorelistic palettes on LCD drivers-
I might be wrong, but I guess that such a patch would be rejected since this trick is not strictly connected to the emulation of the real system...