paint-mixing
Three painter's questions, answered by the library's Kubelka–Munk model. Colours are estimates for ordinary artist-grade oils, not measurements of any brand: treat every answer as a first pile and judge it by eye.
1 · What do I add?
Describe the pile you have, then say what it needs by eye. The suggestions give an amount as a share of the pile, and the side effects to expect.
2 · Can these tubes reach it?
Every mix of up to three colour tubes plus white, in simple part ratios, is enumerated; the nearest one to your colour is returned as a recipe. The first run for a palette takes a moment.
3 · One shared palette for a value plan
The picture is squinted, cut into value bands and split into masses; one recipe per mass is chosen for the whole plan at once, so it needs few tubes. Example: Vermeer, The Milkmaid, Rijksmuseum SK-A-2344, public domain.