I use the 7 colours of the rainbow which are 3 primary colours ( red yellow blue) and 3 secondary colours (orange green violet) + one which is Indigo. I go from blue to red then red to blue. i am not choosing the colours I will do next as it is establish in the colour technique, i am choosing the hue of each colours i use see more explanations here: https://steemit.com/art/@nadversion56/phoenix-and-the-looking-glass