In real painting world what we do:
- fill a pallet with many colors of paint
- take a clean brush, dab on one or two colors, them go paint on canvas
- clean brush in water or pass on thinner
It would be interesting to have a flat brush ( i think its name is "cat's tongue" ) and beeing able to dab two colors with the same brush, and have a two colors stroke at once, without having to add paint right directly to the canvas.