very interesting idea, from a technical aspect, here's some small things i've noticed:
The middle mouse button isn't a great button to use for unmixing, because on my mouse that actually maps to pressing the scroll wheel which doesn't register half the time, i found it was generally more reliable to just swap colors.
The UI for showing what the primary and secondary colors are are also somewhat tricky, during combat i found myself just running away trying to figure out what color or combination of colors i'm supposed to have? perhaps it'd be more intuitive to use the triangles of keys "1-2-q" and "3-4-e" so you don't have to rotate through a color wheel? on controller that could be a combination with a trigger and a flick of the right stick? or perhaps it'd already help to put the UI elements near the player so you don't need to look away to find the color combination?
Taking damage might also benefit from better feedback, at one point i was wondering if the palettes were indicating my health, or the number of rooms i had left to complete because the hitboxes were a little odd,
Also when i died i respawned in the wall and flew off the map.
Still, a great start ;)