J.H. Brown’s 1864 book Spectropia: Or, Surprising Spectral Illusions promises to show “ghosts everywhere, and of any colour.” It accomplishes this by relying on two simple principles: persistence of vision and complementary colors. Readers are directed to stare at any of the figures for 15 seconds and then turn their eyes to a white surface (or the sky); “the spectre will soon begin to make its appearance, increasing in intensity, and then gradually vanishing,” in the color complementary to that of the stimulus.

Try it yourself.