This is a common myth that dogs are completely colourblind and can only see in Black & White. Dogs actually can see some colour, but their spectrum is limited compared to ours.
Dogs are 'Dichromatic' which means that their eyes only have two cone cells that control the colour perception as apposed to humans who have three. This makes us 'Trichromatic'.
Dogs see the world similar to a human that has a red-green colour blindness.
So when your choosing your dogs next toy...make sure its a blue or a yellow one!!