The idea of mixing colors is fascinating, however, it doesn't add efficiency to the straight-forward method of assigning a letter-pair for a single sticker. In order to memorize two stickers, you still have to memorize two units of information - an object and its color. If you're using PAOish system, or at least for most letter-pairs you have an object and an adjective which you alternate during memo, then it's the same amount of info to memorize as if you were using colors.
What I mean by PAOish system is:
PI = {paint, painted, to paint}, PJ = {projector, projected, to project}, PK = {pike, piked, to pike}, PL = {pile, piled, to pile}, PM = {pump, pumped, to pump} and so on.
so then PI PJ PK PL PM = (painted projector pikes the piled pump) vs (red projector, blue pile, ...).
On the megaminx, there's no easy way to assign a single word to a pair of stickers, mostly because it'll require learning ~3500 words. As soon as I acknowledged that, I stopped trying to invent a supreme encoding/memorization method for minxes and learned a basic one, which I recommend everyone to do
PS congrats on your UWR!