They hadn't noticed anything was wrong at first. They lived their life mostly at night, when there was very little color visible anyway, and their pelt couldn't serve as a guide to the changes either. But gradually, over a few days—or was it weeks? They were not very good at time—it had become apparent that the color had vanished from the world.
This seemed to them like a problem that was beyond them to solve. In fact solving didn't really occur to them at all. It wasn't their kind of game. They merely rolled over and went back to sleep.