Black is associated with evil.  

And people are stupid.

But black dogs face another issue: they’re harder to market. Most shelters feature photos of their animals on a website in an attempt to entice adopters; black dogs are difficult to photograph, and their personalities are often masked in darkness. A 1992 Animal Welfarestudy presented participants with photographs of different colored dogs: 65% preferred dogs with lighter coats. Anthrozoos published a study in 2013 that found “participants rate yellow dogs significantly higher that black dogs on the personality dimensions of Agreeableness, Conscientiousness, and Emotional Stability.” The same study found that participants considered black dogs the “least friendly” -- based solely off of a photograph.

Brown cats have an even harder time getting adopted than black cats.

And people are stupid.

But I didn't realize black dogs are harder to market. Wow.