- Let us leave our old friend in one of those moments of unmixed happiness which, if we seek them, there are ever some, to cheer our transitory existence here. There are dark shadows on the earth, but its lights are stronger in the contrast. (896)
- Of several colors, all equally white, that will look whitest which is against the darkest background. And black will look intensest against the whitest background. And red will look most vivid against the yellowest background; and the same is the case with all colours when surrounded by their strongest contrasts.
- Leonardo da Vinci, The Notebooks of Leonardo da Vinci compiled from the original manuscripts by Jean Paul Richter, (1970) 150.