Did you know that pigeons are pentachromats, meaning they have five color receptors in their eyes? Most birds have four, humans of course have three. It is estimated that pigeons can see over 10 billion different colors (humans see about 10 million). So while we see pigeons as shades of gray, they most likely see themselves in all manner of impossible hues and colors we will never even know. Color is no doubt important to birds, and bringing out your adoptable pets colors in their photos can be important to getting them noticed online.

Dillon
Keeping that color wheel in mind you remember from grade school think about complementary colors (the colors opposite each other on the wheel) and analogous colors (the colors next to each other). Nature actually gets this color harmony right most of the time, so the only thing you need to do is consider the background you place your pet in.
Check out Dillon from Patty’s Parrot Place for an example. His vibrant green surrounded by the yellow-orange walls and the blue threaded rope, all analogous colors. Analogous colors are easy on the eye, and common in nature.
Complementary colors create much more contrast, but that can be useful to help your pet stand out. Loki from the Best Friends Animal Society is showing split-complementary colors in his photo. This is when the colors are not direct opposites, but just off by one on the wheel. The blue wall compliments his reddish comb and yellow beak and helps them to stand out.

Loki
You can apply this principle to black and white as well. Here a bright white cockatoo named Coco from the Humane Society of New York is brought into crisp detail thanks to the contrasting black background.

Coco