Swatching – in knitting this practice helps see how colours work together, by knitting small samples.  But I can also see how this theory would help with painting and other arts and crafts of colour (especially patchwork).

There’s a master class in this whole area from Shetland knitter Ella Gordon on her blog, right here: https://ellagordon.wordpress.com/2016/06/30/crofthoose-hat-knit-a-long-choosing-colours/

With the colours of Shetland wool which are delicious, almost edible, it would be hard to go wrong: