Gamboge

In Southeast Asia it was and is used to dye the robes of Theravada Buddhist monks. The saffron colour of monastic dress is usually this rather than actual saffron, which would be unaffordable at that scale. So a colour the West reads as 'Buddhist' is a specific tree resin from a specific region.

It reached Europe in the seventeenth century and became a staple watercolour yellow through the eighteenth and nineteenth: transparent, easy to handle, and a clean warm yellow. Turner used it. So did most of the British watercolour school.

It is also a violent purgative, which was known and exploited medicinally. There are recorded cases of painters made ill by it, and the standard advice not to put a watercolour brush in your mouth has this pigment somewhere in its history.

Monastic robes, watercolour, wood stain and lacquer, and gilding-adjacent work where a transparent gold tone was wanted over metal leaf, gamboge over silver leaf reads convincingly as gold, which was a standard economy.

That last trick is worth stealing. A transparent warm glaze over a cool metallic reads as a more expensive metal. The same principle is behind gold-effect printing, warm varnish over silver foil, and most convincing fake brass. Transparency over a reflective surface is a cheap route to an expensive-looking result, in print as much as in paint.