If it’s all the same to you, choose blue and yellow toys for your cats. Those are the colors that stand out to them. A red ball on green carpet, on the other hand, will look kind of like the first 20 minutes of The Wizard of Oz — shades of drab that don’t stand out. It’s because cats have fewer cones in their eyes than we do. They evolved learning to hunt in low light, so differentiating between colors was not very important for survival.