Dogs Eyesight

[soobet]

How can they say Dogs are colourblind?
Its not as if they can tell us is it?

[Quizmonster]

Colour vision is controlled by cones - light-sensitive parts of the eye - of which dogs apparently have only two types rather than three. Consequently, they are, it seems, red/green colour-blind...as are about four in a hundred human males. It is the absence of the necessary cones in dogs' eyes that enables scientists to tell that they are partially at least colour blind.

[spudqueen]

I remember seeing a film many years ago in which a dog was trained to recognise a red card as treat time and a green card as sit. They gradually made the red and green the exact same tone, so that in black and white you could not tell the difference and the dog could not tell either.