Have you tried different food?
Attempting to eliminate the stains is a post cause. Kinda like treating a spaghetti stain after your kid has spilled it on their shirt. Best path is prevention and to find the cause may take time and experimentation.
I have read somewhere that too much iron in the food will manifest in "rust" type stains around the mouth and eyes. I do not know for a fact. Some dyes used in food or treats will cause the same effect.
Attempting to eliminate the stains is a post cause. Kinda like treating a spaghetti stain after your kid has spilled it on their shirt. Best path is prevention and to find the cause may take time and experimentation.
I have read somewhere that too much iron in the food will manifest in "rust" type stains around the mouth and eyes. I do not know for a fact. Some dyes used in food or treats will cause the same effect.