Our tri became allergic to grass a year or so ago. His hair was falling out where the grass touched his body where he laid in the yard. He also has food allergies.
Our Vet put him on Iams Kangaroo & Oats, which he did really well on. The downside was the food had a lot of chemical additives and was $70 for a 25 pound bag, could only be bought through our vet.
A strange thing happened though after about 4-5 months on the food. He developed like orange brown bat wing like marking on his shoulders. I kidded our kids that he was growing shinigami wings, (he does have the devil in him), or the kangaroo meat was changing his color as meat kangaroos are often the Red Kangaroo (half joking).
Anyway, we switched his food to Blue Buffalo Lamb & Rice, which he is doing well on. After about 3 months his little wing marks disappeared.