“Dogs have two cones—one with a long, yellow-green opsin and another with a short, blue-violet one. They see mostly in shades of blue, yellow, and gray. When my corgi Typo looks at his red-and-violet toy, he probably sees the red as a dark, muddy yellow, and the violet as a deep blue. When he looks at the bright-green ring that he likes to chew, the green stimulates both his cones equally. Because of opponency, those signals cancel out, and Typo sees white. Horses”
―
Ed Yong,
An Immense World: How Animal Senses Reveal the Hidden Realms Around Us
