I found out that OLEDs on my Intuos4 Wireless are actually 4-bit colour instead of 1-bit. I don't know (yet) a method of setting 4-bit icons over bluetooth, but I have a proof that it can be done over USB. The proof:

Intuos4 Wireless 4-bit OLEDs

It's close up of one of the OLED displays on Intuos4 Wireless connected with USB cable.