Skin Tone tool
The Skin Tone tab of the Color Editor in Capture One is built to make skin tones even and natural. You pick the skin colour and the tool pulls blotches and colour shifts within that tone closer together. The result is smooth skin without the plastic look.
The 'Hue', 'Saturation' and 'Lightness' sliders steer the whole skin colour, while 'Uniformity' reduces variation within the skin. Pick the skin with the eyedropper and widen the range a little so shadow and highlight areas are included. Work on a separate layer with a mask on the skin so the rest of the photo stays untouched. Tip: go easy on Uniformity, a little keeps skin natural, too much makes it flat.
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The presets on this site set these adjustments up for you as a starting point, which you then fine-tune to taste.