r8748 /src/mess/drivers/pc6001.c: [PC-6001]: Emulated gfx mode 4 user-selectable colors

You can select between monochrome (default):
[Linked Image from mamedev.emulab.it]
Red/Blue
[Linked Image from mamedev.emulab.it]
Blue/Red
[Linked Image from mamedev.emulab.it]
Pink/Green
[Linked Image from mamedev.emulab.it]
Green/Pink
[Linked Image from mamedev.emulab.it]

Oddly enough, vram data is exactly the same, I'm actually thinking that the monochrome mode is actually still in 2bpp but uses shades of gray? It's unlikely since other emus emulates this like I've done, but ... (needs original refs to confirm)