Just when I keep leaving the paint/color stuff I keep going back. This is FireAlpaca – a free paint tool for Windows and Mac.
It’s very fast: one of the things I like about Paint NET is that it’s very fast with everything and FireAlpaca is just as fast. Just messing around for 2 minutes, using something they call “Edge Pen” (I made it wider) and using paint bucket to fill stuff in, I ended up with some abstract thing that doesn’t look horrible. This I could probably work with regularly.