When I switched fron RC puppy to the RC yorkie blend Gizzie would wake up and vomit bile but only in the morning....Strange. But i bought some baby food(make sure it does not contain onion powder) and as soon as she woke up i would give her about 2 tbsp. just to get something on her tummy so when she would eat the RC her tummy wasnt totally empty. Anyway the vomiting only lasted about 4-5 days. I did not mix the food when I switched her so it just upset her tummy. She also has firm dark stools but i would rather see that than diarrhea
Good luck!!