I'm not sure how to explain it, but from time to time, and even in some of your paintings, while studying the skin tones and colours used you don't often see just light and dark versions of the local colour, but greens, blues, purples. As a general rule I realise that if a highlight is a light cyan the shadow is some kind of purple, loosely, but I'm not sure where to apply the reds, greens and yellows on the skin accurately..
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