Two Colours, one whereof serves for a Ground to the other, whether they be illumined, or suppos'd in a Shadow, will appear free and loose from each other, in proportion as they are found in different Degrees; That is, one Obscure Colour must never serve as a ground for another; but for that Use you must chuse some very different Colour, as White, or some other Colour bordering in the same Degree upon White, as the other appears bordering upon Black.