Pour. Mix. Transmute.
1Tap a vial, then tap another to pour the top color. Same color on same color only, and a full pour must fit.
2Enchanted flasks transmute. Pour either of a flask's two catalyst colors in and it lands as a brand-new third color. Finish the flask in that color.
3Sort every vial to one color to clear the level. Fewer moves, more stars.