How do I make yellow or green?

[CrazyCatBird]

You could try this brush to start with (saturated colors seem to work best)
RGBA-Mix brush … You should press firmly to cause more color, then gradually lessen the pressure to cause mixing… It takes practice.

… And then there’s this mode:

Whale using Krita 5.x and parallel brush blending mode

I just discovered the interesting parallel blending mode available in Krita 5.x. I feel it helps render a watercolor look yet allows me to paint light on dark when needed. The blending mode is applied to the brush itself, not the layer. [whale-1-1536]