Colo(u)r wheel in widget

I have a png of a colo(u)r wheel within a canvas and I want to fragment the canvas in a very particular way so that selecting each section can activate a different material ID. How would I go about fragmenting a canvas panel in such a way, and if it’s not possible, what method should I use. I am very set on using this particular format for the colo(u)r wheel.
Cheers in advance!

The easiest way to do it would be to have a separate button for each part of the color wheel.

So to the user, it just looks like a color wheel, but we secretly know it’s a lot of transparent buttons arranged in a circle.

Then you can just set the color by which button they press.