Do dogs really see in black and white only, or can they see certain colors? Have any "color blindness tests" been done on dogs? One possible test I see is to train a dog to point to a pattern, and then embed that pattern in different colors (equal brightness) and see if they "point to the pattern" among other solidly colored cards to find out.
Dogs in general are not color blind, but they see fewer colors than we humans. Dogs see can shades of blue and yellow. Here's a study that talks about it. http://www.smithsonianmag.com/science-nature/new-study-shows-that-dogs-use-color-vision-after-all-13168563/?no-ist
No, dogs do not only see in black and white.
Humans' colour perception is trichromatic (our eyes have cones sensitive to each of the colours red, green and blue); dogs' is dichromatic (theirs have cones sensitive to each of yellow and blue).
Their ratio of rods to cones is higher than ours, but the conclusion that they do not perceive colour as brightly as we do may not be accurate. Researchers in Russia found that for eight previously untrained dogs colour was more informative than brightness when they were choosing between stimuli that differed in both brightness and colour.
I am not convinced that it would be right to conclude that dogs cannot perceive red as a colour or at least cannot distinguish it from green and yellow (which would in humans be a form of colour blindness). I have a friend whose dog treated all red vans, and vans of no other colour, as if they were post vans.