Same here. It's wild that such a good program is FOSS.
That's the color picker, and it's only step one. Step two was adjusting the hue and saturation. For this case I treated the lights as cool colors, the shadows as worm colors, and assumed no bounced light beyond a little sub surface scattering from Kaelyth's (hopefully) red flesh. As such I adjusted the shadow colors to be closer to red by about 2-5 degrees and boosted the saturation. By default pressing the /K/ key will do this for you, but I tend to boost the saturation even more for stylized work.
The final colors and blending I got by
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with the basic-2 Opacity brush and picking the intermediary color (hold ctrl and tap with your stylus). Admitingly there's a few areas like where the pecks meet the boobs where the airbrush or blender blur would make things easier, but I wanted to rub in the fact that you don't nessisarily need either of them.
You flatter me! I'm an intermediate at best. Still, I don't mind sharing what I learned over the past decade or so.