The yellowing of the white hair on the cat's belly may be related to the cat's hygiene and diet. If the cat has been active in a dirty environment for a long time and has not been bathed for a long time, the hair will turn yellow and dirty. The cat needs to be bathed and cared for regularly. Hair. If a cat eats food that is too oily or salty for a long time or lacks nutrients, it will also cause the cat's hair to turn yellow. The cat's diet needs to be adjusted to supplement nutrition.