What does it mean if my cat’s poop changes color?

Healthy cat stool is some shade of brown, and the exact shade shifts a little with diet, which is normal. A one-off lighter or darker stool after a food switch is rarely a problem. What is worth acting on: black or tarry stool (can mean bleeding higher in the digestive tract), pale gray or clay-colored stool (can point to a liver or bile issue), or red streaks of fresh blood. Those three colors are the ones that separate a diet-related shift from something that needs a vet visit, not the difference between medium and dark brown.

When to call a vet: Black, tarry or clay-colored stool is a same-week vet visit, not a wait-and-watch situation.