It is currently possible to change the color of multiple keycaps at once using their category (alphas, mods and accents). The same result can also be achieved by manually selecting multiple keycaps, but this acts differently as you can't re-select those same keycaps later. So if you have a couple of special keys, you to manually select them every time you want to edit their colors.

In order to provide a better UX, I would like to be able to change the category in which a keycaps is and/or add more categories. For inspiration, this is what keyboardsimulator.xyz is calling "swatches". That way, I can select a few keys, redefine their category, edit the color of that category whenever I want and it automatically applies to all keys that are grouped using the same label.

For added context, I don't see myself using more than 5 categories, maybe 7 or 8 if you want to make a fancy gradient.