A Treatise on Painting/Chapter 232
Chap. CCXXXII.—Of lively and beautiful Colours.
For those colours which you mean should appear beautiful, prepare a ground of pure white. This is meant only for transparent colours: as for those that have a body, and are opake, it matters not what ground they have, and a white one is of no use. This is exemplified by painted glasses; when placed between the eye and clear air, they exhibit most excellent and beautiful colours, which is not the case, when they have thick air, or some opake body behind them.