Colour contrast diagrams from 'De la loi du contraste simultane des couleurs et de l'assortiment des objets colores' (The principles of harmony and contrast of colours) by the French chemist Michel Chevreul (1786-1889). These diagrams show how vividness of a colour effects its surrounds. When looking at colours on a white background a halo of complementary colour is perceived around the colour, wich is proportional to the colour's brightness. This occurs because the brain exaggerates differences in hue and brightness, making juxtaposed colours appear more different than they actually are. This phenomenon is known as simultaneous contrast.