It's so true to stay away from foods with dyes in it. But other than that, each food seems to affect each dog differently. I suspect allergies. When I got Jett 7 months ago, he had some staining. I put him on the same food as Zoe, whose face was perfectly white. His staining stayed the same. He developed IBS, had to put him on a low residue food. So I put both of them on the same low residue food. His staining got better...and her once perfectly white face became stained.
So now I have her back on her old food and him on the low residue food and both faces are having less staining. However Jett is no longer satisfied with his food. Argh!!!