Ah they look blue plus the name..haha. I have a couple black cats; my biggest cat is solid black; a great cat too. I do have a cat that if she were able to she'd eat herself to death. Literally. Maybe boil a chicken and start giving them that in a bowl a couple times/day and cut back a little on the dry food. The pure protein might help them feel full longer and they won't crave that dry kibble as much. If they're happy and Blue is a food addict I wouldn't stress them by changing their diet.