English: This is a possible layout for basic colour-to-colour transitions, trying to answer the question: how to seamlessly transition among colours in a 2D space?

Given 8 basic colours: black, red green, blue, yellow, magenta, cyan and white, there are 8 * 7 = 56 possible transitions between any two of them.

The basic colours are represented with circles and the transitions with lines. For simplicity the lines are uniformly coloured with the average of the two colours that they connect.

This image shows a pair of graphs that cover together all 56 lines, once and once only, without having any two lines intersecting.

In a 3D space, the graph on the left could be shaped into three tetrahedrons (attached by their white/black side) and the graph on the right could be shaped into an octahedron, giving a total of 4 * 3 + 8 = 20 triangular surface areas, which would be a small selection of the 8 * 7 * 6 = 336 possible ones.