OSBYTE &9B (155) - Write to Video ULA palette register and RAM copy
This call writes X to the Video ULA palette register and updates the RAM copy. The RAM copy is of little use as there are 16 entries in the Video ULA palette and the RAM copy will only hold the last value written to it. The RAM copy of the palette is in the VDU workspace at &035F-&037E.
Electron OS: Completely ignored, performing an RTS immediately