The Verification Venue · pointed at a thing everyone gets wrong
The Colours the Dog Keeps
Your dog is not colourblind, and it does not see the world in grey. It is a dichromat — two kinds of colour cone instead of your three — and that is a precise optical fact, not a vibe. From the two real cone curves you can compute exactly which colours collapse together for a dog, and which it keeps.
A human retina has three cone pigments; a dog has two, with measured peaks at 429 nm (a blue cone) and 555 nm (a yellow-green cone). Missing the long-wave "red" cone you have, a dog can't separate red from green: the whole warm half of your spectrum drives its two cones in nearly the same ratio, so it folds into one hue. Below, both cones are drawn from the published visual-pigment template keyed to those two numbers — nothing is hand-painted. Drag the wavelength and watch.
Blue cone (429 nm)
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Yellow cone (555 nm)
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Dog hue = S/(S+L)
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The dog's whole sense of colour rides on one number: the fraction of the signal coming from the blue cone, S/(S+L). Two lights with the same fraction are the same colour to a dog, however different they look to you. There is one wavelength — the neutral point, which the math below puts at ~484 nm, right where Neitz measured ~480 nm — whose fraction equals that of plain white light. A dog cannot tell that wavelength from grey.
Pick a colour — see it in dog-vision
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Try red, orange and green in turn: the dog-view barely changes, and the three land almost on top of each other on the hue bar. That is the red-green collapse, computed — not an artistic guess. Now try blue: it jumps to the far end. Blue is the colour a dog keeps.
The check — every number recomputed in front of you
The two cone curves are the Govardovskii 2000 A1 visual-pigment template evaluated at λmax = 429 and 555 nm — the peaks Neitz, Geist & Jacobs measured in three dogs. The template is normalised to 1 at each peak (the cross-check), and the neutral point falls out near the measured ~480 nm.
| quantity | computed live | measured / expected |
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For the colour you've picked, its two cone signals and the single dog-hue, computed from the same weights the verifier uses:
Run it yourself — the script rebuilds the cone curves from scratch and recomputes every figure above: node research/the-colours-the-dog-keeps/verify-the-colours-the-dog-keeps.mjs
What's idealised here, and what's exactly true
Exactly true. The dog retina has two cone classes, peaking near 429 and 555 nm — that is a behavioural and electrophysiological measurement (Neitz, Geist & Jacobs 1989), corroborated since. With only two cones, colour vision is one-dimensional in chroma: every light reduces to a single S:L ratio, so any two lights sharing that ratio are physically indistinguishable to the dog. The red-green collapse and the existence of a neutral point are exact consequences of having no long-wave cone — not stylistic choices.
Idealised. (1) The cone curves are the Govardovskii 2000 template, a published shape that fits real pigments well but is keyed only by the peak wavelength; the true dog curves differ slightly in width. (2) To recolour an arbitrary on-screen pixel we model your display's R/G/B primaries as narrow Gaussians (centres 611 / 549 / 465 nm) — a stand-in for the real, slightly broader primaries; the red-green collapse does not depend on their exact width, but the precise dog-hue of a mixed colour does shift a little. (3) The neutral point is defined against an equal-energy white; a different white (daylight, a screen's white) moves it a few nm.
Small sample, real variation. The peaks come from three dogs plus electrophysiology; individual and breed variation exists, and ageing lenses yellow and shift sensitivity. Take 429/555 nm as the well-supported central values, not a per-dog guarantee.
What this is not. The dog-view image is a model of which colours a dog confuses, mapped back into colours you can see on a trichromat screen. It is not a window into canine qualia — "sees yellow and blue" is shorthand for the two-cone axis, not a claim about what the experience is like. Brightness and contrast processing differ too, and dogs out-resolve us in dim light; none of that is in this colour-only model.