Honestly you can get like 80% of the way there by just doing a lot of smooth gradients and putting a little noise over it, it's trivial once you stop thinking i

Honestly you can get like 80% of the way there by just doing a lot of smooth gradients and putting a little noise over it, it's trivial once you stop thinking in terms of "manipulating a virtual paint-depositing tool" and start thinking about what it looks like on the illustration board. Turning a gradient into an emulation of a more deliberately-uneven, splattery, and possibly drippy application of paint is a bit more complex though.