There’s a commonly held belief that dogs only see in black and white, but that's simply not true. They definitely see quite a bit more than just black, white, and grey. They do, however, have only two colour receptors, or cones, in their eyes, while humans have three. So in fact, measured in human terms, dogs are technically colourblind.
What does this mean? Basically, dogs can’t see red or green, and they can't perceive variants of those colours, like orange, pink, or purple. Nor can they perceive subtle changes, such as in brightness, or in shades.
Have you ever found that there are times when you throw a ball or a stick, and your dog can’t find it in the grass? That’s because it’s in a colour they can’t distinguish; because they just don’t have our full-colour spectrum. Dogs are essentially limited to a spectrum of yellows, blues, and violets – and don’t have reds, greens, and oranges in their colour palette. Those colours will appear to them as variations of yellow and blue.
Like human beings, a dog’s eyes have retinas made up of rods and cones (the two photoreceptors). We have more cones than dogs and they have more rods than we do. But they don’t have fovea, which is the small, central pit we possess, composed of closely-packed cones essential for sharp visual detail; and as a result, dogs see things in far less detail, equivalent to us seeing everything rather badly out of focus.
And yet, their night vision is way better than ours, and they can track movement much better than we can. For example, if you were to throw an orange ball onto a green lawn, that would look like yellow-on-yellow to your dog. But his wonderful ability to perceive movement is what would help him find the well-camouflaged ball.
It might come as a relief to know that your dog doesn’t ever judge your dress-sense because all your outfits probably look the same in their eyes! But they’ll always recognise the colours in your voice...