Purple

Under Rayleigh scattering, violet light scatters more than blue because shorter wavelengths scatter more. Yet the sky looks blue, not violet: the sun emits little violet light, and our blue cones are much more sensitive than violet ones.

One of the first mass-produced purple synthetic dyes came from a failed malaria-drug chemistry experiment. In 1856, 18-year-old William Perkin tried to synthesize Quinine and found a dye for silk.

A giraffe's tongue reaches 45–53 cm with a tip colored deep blue, black, or purple. The dark hue comes from melanin, and the leading explanation is ultraviolet protection: giraffes spend 16–20 hours browsing with the tongue out, so its most exposed part needs sunscreen.

Purple does not exist in the light spectrum. When red and blue light simultaneously stimulate the eye, the brain creates this color to resolve the contradictory signals.