“Assuming with Euler that colours are isochronous vibrations (pulsus) of the aether, as tones are of the air set in vibration by sound, and, what is most important, that the mind not alone perceives by sense their effect in stimulating the organs, but also by reflection, the regular play of the impressions, (and consequently the form in which different representations are united,)—which I, still, in no way doubt—then colour and tone would not be mere sensations. They would be nothing short of formal determinations of the unity of a manifold of sensations, and in that case could even be ranked as intrinsic beauties.

But the purity of a simple mode of sensation means that its uniformity is not disturbed or broken by any foreign sensation. It belongs merely to the form; for abstraction may there be made from the quality of the mode of such sensations (what colour or tone, if any, it represents). For this reason all simple colours are regarded as beautiful so far as pure. Composite colours have not this advantage, because, not being simple, there is no standard for estimating whether they should be called pure or impure. . . .

To say that the purity alike of colours and of tones, or their variety and contrast, seem to contribute to beauty, is by no means to imply that, because in themselves agreeable, they therefore yield an addition to the delight in the form and one on a par with it. The real meaning rather is that they make this form more clearly, definitely, and completely intuitable, and besides stimulate the representation by their charm, as they excite and sustain the attention directed to the object itself.”

—Immanuel Kant, “Analytic of the Beautiful” from The Critique of Judgement, 1790. Translated by James Creed Meredith.