Colour theory
A colour wheel made of tubes, not light.
The wheel printed in most books is a diagram of hue angles. It tells you where violet sits, but not that ultramarine and magenta make a dull violet while phthalo blue and magenta make a much cleaner one. Every wedge below is computed from real pigment data with a Kubelka-Munk model, and each one names the tubes it came from.
The twelve hues
Selected wedge
Yellow
#FDDE10
Cadmium Yellow straight from the tube.
Single tube: Cadmium Yellow.
Tinted with white
How to actually use it
Pick the primary that leans your way. Every mix runs through the bias of the tubes you start with. For a clean green you want a blue that leans green, so phthalo rather than ultramarine. For a clean violet you want a blue that leans red, so ultramarine rather than phthalo.
Opposite wedges kill each other. Sitting across the wheel is the shortest route to a believable grey, and the result keeps some of the parent colour rather than going flat the way black does. The complementary colours guide shows how far to push each pair.
The wheel hides value. Two wedges can share a hue and read completely differently on the canvas because one is three steps darker. Judge value first, hue second.
Want the full grid?
The interactive colour mixing chart shows every pair of ten common tubes at once, and you can print it.