This seems like a good idea, but primary color mixtures tend to look less saturated and less bright than individual pigments.

That’s just how it works: pigments absorb certain colors of light and reflect others, and absorption dominates reflection. In other words, two pigments mixed together absorb more light than a single pigment, even if the visible color is the same.

Saturation and brightness are key for graffiti art, especially because colors tend to fade over time. Graffiti artists also use metallic colors like chrome.

The device claims to solve the problem of having to carry lots of paint of different colors, but practically that is not an actual problem: artists usually decide their color scheme beforehand, and choose the paint they carry based on that and an approximate volume required.

Still, being able to cover a surface with paint is more important than being able to do it with an exact color. Volume is more important than color. If you run out of one color, you improvise with the other colors you still have.

That is not possible if you always need to have all primary colors available to produce the color you need. You might end up having to carry more paint, but still end up unable to finish a piece.

All in all, it seems like a complex solution in search of a simple problem.