Do dogs really see in black and white?

No. Dogs see colour, just less of it than people do. The black and white claim has been repeated for decades and is simply wrong.

Human colour vision is trichromatic, relying on three types of cone cell sensitive to short, medium and long wavelengths. Dogs are dichromatic, with two types. The practical result is comparable to the most common form of human red-green colour deficiency: dogs distinguish blues and yellows well, while reds, oranges and greens are difficult to separate from one another and tend to appear as shades of yellow, brown or grey.

That has a mildly useful consequence. A red or orange ball on green grass, which is vivid to us, is poorly differentiated to a dog and is located largely by scent and movement. A blue or yellow toy stands out considerably better.

Colour is also not where canine vision is strongest, which puts the deficit in perspective. Dogs substantially outperform humans in low light, thanks to more rod cells and a reflective layer behind the retina that gives light a second pass, which is also what causes eyeshine in photographs. They detect motion better, and many breeds have a wider field of view.

Where they do worse is fine detail. Canine visual acuity is considerably lower than human, so a dog recognises a familiar person at distance by gait, outline and scent rather than by facial detail.

The broader point is that dogs experience the world primarily through smell, with vision as a supporting sense, which is close to the reverse of the human arrangement.