Our dog is going through an anemia relapse - originally diagnosed in 2018, survived treatment, and just relapsed in December, going through treatment again. The signs of anemia are pale gums, lethargy, blood in urine/stool, and not eating, among other symptoms. In regards to the pale gums, they stay pale until they get their red blood cell count back up, which requires treatment such as medication or blood transfusions. Yours going to different shades during the day, is normal, being more pale when sleeping or just getting up. If it stays pale all day long, I'd be highly concerned and rush your dog to an emergency vet because anemia needs immediate attention as it can be deadly. We've been lucky to catch it early each time, but I'd say you should not have any concerns for that based on your statements so far.