I think the NES PPU:CPU clocks are 3:1 for NTSC and 16:5 for PAL. The exact speeds are integer ratios of the color subcarrier frequency. The master clock runs a

I think the NES PPU:CPU clocks are 3:1 for NTSC and 16:5 for PAL. The exact speeds are integer ratios of the color subcarrier frequency. The master clock runs at 6x the color subcarrier frequency, which gives you 12 different hues in the color palette.