To dither finely the 8 RGB colours cannot produce more than 27 colours because of redundancy in the result colour from diferent combinaison.
*Opposite colours from the 2x2 2x2x2 (1bit) RGB cube would produce grey
Ex : Black + White = grey, Yellow + Blue = Grey.
*some other mix would produce already existing basic colours
Ex : Red + Blue = Magenta, Red + Green = Yellow.
*would only remain :
= 6 intermediary colours : Lime, sky blue, Purple, Sea Green, Orange, Lavender.