A flower has more than one face.
Flowers and the eyes that see them have evolved together for roughly 120 million years. Many of them carry ultraviolet honey guides — concentric patterns invisible to us, but glowing like landing strips to a bee. Switch between the six eyes below — from a whale that cannot see colour at all to a mantis shrimp with twelve photoreceptor types — and feel how the same sunflower changes meaning depending on who is looking.
Three cone types peaking at 420, 534 and 564 nm. We see roughly 380 to 700 nanometres. Bright yellow petals, a chocolate-coloured disc, a green stem. Familiar, complete — but the picture is missing whatever lies below 380 and above 700.
The flower is a stylised vector illustration; its colours change between the six modes to suggest how each eye perceives the same object. Bee mode shifts UV-reflective regions toward an artificial violet so we can see them on a normal RGB screen — bees do not actually see this exact colour, but the contrast pattern is the real one documented in UV photography of Helianthus annuus. Bird mode hints at the fourth channel via subtle UV-fluorescent overlays. Dog mode applies a deuteranope colour collapse. Whale mode strips chroma entirely to render the single-cone monochromat experience. Mantis shrimp mode rotates the hue per petal to suggest the spectral richness of twelve narrowband channels — strictly schematic, since no RGB screen can show twelve-dimensional colour. The spectrum chart shows real peak sensitivities from Bowmaker & Dartnall 1980 (human), Peitsch et al. 1992 (bee), Hart 2001 (songbird), Neitz et al. 1989 (dog), Peichl et al. 2001 (whale) and Marshall & Oberwinkler 1999 (mantis shrimp).
Four answers to one selection pressure.
Why bees see ultraviolet.
Insect colour vision predates flowering plants by hundreds of millions of years — the UV photoreceptor is part of the basic arthropod toolkit (Briscoe & Chittka 2001). When flowers diversified in the Cretaceous, those that broadcast a bee-visible signal got pollinated more reliably. UV honey guides are the direct visible result of that coevolution. The flower is, in a real sense, advertising in a language the bee already spoke.
Why birds have four channels.
The common ancestor of all vertebrates had four cone types. Birds — sauropsid descendants of dinosaurs — kept them. The fourth, ultraviolet/violet channel helps them find ripe fruit against leaves, evaluate plumage of potential mates, and read structural colours invisible to us. Add coloured oil droplets in front of each cone (Toomey & Corbo 2017) and a bird's colour vision is, on most measures, the richest among vertebrates.
Why most mammals see less.
Early mammals were small nocturnal creatures during the long age of dinosaurs. Two of the four ancestral cone types were lost — colour vision is expensive and worthless in the dark. Most mammals are still dichromats today: dogs, cats, horses, cows. The world they see is not impoverished from their point of view; it is simply optimised for movement, contrast, and low light rather than for colour.
Why we are the exception.
Old World primates re-evolved a third cone roughly 30 million years ago, most likely to spot ripe fruit and tender leaves against the canopy (Surridge et al. 2003). We sit on the high end of mammalian colour vision but well below the avian and many insect baselines. The honest summary: among the eyes on this page, ours is neither the simplest nor the richest. It is the one we happen to use.
The extremes — from nothing to twelve.
At one end of this page sits a whale: a mammal that gave up colour entirely on its way back into the sea. At the other sits a mantis shrimp with twelve photoreceptor types — and worse colour discrimination than we have, because it labels with its channels instead of mixing them. The lesson is not "more receptors are better". The lesson is that each eye is optimised for the specific task its owner needs to solve. The whale needs contrast at depth, not red versus green. The mantis shrimp needs a fast classifier for whatever shimmers past its burrow. Our trichromatic system is one solution among many, and not always the best.
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- Hart, N. S. (2001) — The visual ecology of avian photoreceptors. Progress in Retinal and Eye Research 20.
- Neitz, J. et al. (1989) — Color vision in the dog. Visual Neuroscience 3.
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