I'm usually one of those painters uses the same brush, wipe it off, a swish of mineral spirits and back in. Mix one color and then shift it to another color. The brush starts out painting the blue of a sky and ends up with some dark colors in shadows. And I always had trouble with changing a color already laid down - a tendency to grey down even parts I wanted to hold color.
Some long while ago I saw one of Marc Dalessio’s public videos and remarked to myself that he held a pile of brushes in his left hand while painting. At the time, I thought, "That's weird, everyone else holds a roll of paper towels." But the image stuck in my mind, even though for many months trying to remember who it was, I kept thinking was Frank Serrano. But no, it was Dalessio.
A couple days ago that image was so compelling I tried it for no particular reason and found myself picking out a new brush for each color change. What a difference! I'm kind of loose and ramshackle about my painting habits so no telling if I will stick with it as perfectly as he, but it DOES make a difference.
So, thank you, Marc !