The development of colour vision in animals

[Catherine]

I am sure dogs see colours. They may not see them exactly the way we do. We don't all see colours in the came way. I am not talking about colour blind people. They lack colour receptors or at least some colour receptors. Some people with colour vision do not seem to see the depth of colours. They see green as green. Some people can distinguish tiny variations in colours. A few drops of blue in the green makes it a whole different colour for them.

Maybe dogs are the same. Many dogs would have to be observed before we would know what they see. 
Clearly your Jack Russell, Toby could see orange and distinguish it from yellow and red. I can understand him not looking at the apples. They are different in shape, but the grapefruit is very much like and orange. He was going by the colour.

I think we have just scratched the surface of studying colour vision. The world is full of colour so it is safe to say that colour must have played a part in evolution. Too many insects have vision that is geared to seeing the special colours that they need to see. Bees have very complex relationships with plants and they have very complex vision to see the colours that plants exhibit to the bees that they rely on for pollination/fertilization. That is a whole field of study in itself.