Sad preacher nailed upon the coloured door of time

The spider known as Adanson's house jumper has excellent colour vision, with three opsins (visual pigments), which makes them trichromatic, like us - but unlike us, the spiders have two opsins for visible light and one for UV. Dragonflies have as many as 30 opsins. But as the mantis shrimp demonstrates, more visual pigments doesn't necessarily mean seeing more colours.

Human eye proteins detect red beyond red (New Scientist, 6 December 2012)

Colour: The Spectrum of Science (site for the BBC Four show)

Magnet triggers colours in 'blind' man's brain (New Scientist, 28 October 2008)

Paletton Color Scheme Designer

Coloradd, "a sign code for aiding color blind people to recognise colors"

Optical illusions show how colour can trick the eye (The Age, 1 March 2015)