No, dogs do not see in black and white: they perceive colors, but dichromatically. Their retina only distinguishes shades of blue and yellow; red and green appear to them as indistinguishable tones of gray or yellow-brown.
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A retina with two cones instead of three
Colored vision depends on the retinal cones. Humans have three types, sensitive to red, green and blue (trichromatic vision). The dog only has two, based on blue-purple and yellow-green. Red and green activate the same receptors and merge, a bit like in a colorblind person with deuteranopia.
What the dog loses in color palette, he largely gains elsewhere. Its retina is rich in rods, cells dedicated to detecting dim light and movement rather than color. It is lined with a tapetum lucidum, a reflective layer behind the retina which returns uncaptured light to the photoreceptors: it is this which produces the characteristic reflection of the dog's eyes at night and allows him to see much better than a human in dim light. The dog also detects rapid movements much better than a fixed object of the same color, a direct inheritance from its hunting ancestor.
The red toy, invisible on the grass
This dichromaty has a very concrete consequence for the choice of accessories: a red ball placed on a green lawn appears in almost identical tones to the dog's eyes, because red and green merge in its visual spectrum. The animal then locates it mainly thanks to movement or smell, not to color. Conversely, a blue or yellow toy stands out clearly against a green or brown background and remains identifiable even when stationary. For a game of fetch or visual search, favoring blue objects rather than red therefore really makes it easier for the dog to spot them.
