Why does dog hair turn reddish brown?

Every time a long-haired dog urinates, there may be urine on the hair, causing the hair to become yellower and yellower, and cannot be washed off even if you take a bath. It may also be that you didn't blow dry after taking a bath. The moisture on the coat will also cause oxidation of the hair. The owner can wipe the dog with a wet paper towel after urinating to keep the coat dry.