ULAplus is a specification for a proposed hardware replacement for the Spectrum ULA. The current specification includes four colour modes:
0 - original spectrum behaviour
1 - RGB (see ZX Spectrum 64 Colour Mode)
2 - HSL (not yet finalized)
3 - CMYK
Any hardware implementing ULAplus must implement at least mode 0 and one other mode to be considered a ULAplus device.
G3R3B2 encoding
Offset H(S)L encoding
CMYK (little-endian) encoding