A healthy tongue is a nice red, free from cracks or raised/sunked areas, no coat.
While cleansing, it is common to see some disturbances as things shift about. The FAQ goes into some detail. It's improtant to check the tongue every morning to check in and make sure you digested everything the day before. If the tongue is coated, you have "ama" or undigested food particles in your digestive tract, which, if left there so that they get absorbed, is what coats the veins, causes arthritis, chronic illness. You ahve to drink ginger tea and take fiber or get a colonic and flush them out.