My tongue is yellow randomly now. it's been a few months. why? i drink gallons of water a day and i am pretty healthy with food.

Yellow/white tongue: The tongue is known to have many variations with pigmenting, size, appearance, & not always due to disease. Causes of a tongue that looks white include: lichen planus (responds to steroids), white sponge nevus (familial, benign, permanent), smoker's leukoplakia (2% risk of cancer, needs biopsy), hairy leukoplakia (due to epsteinbarr virus), warts (due to papillomavirus), "thrush" (rx antifungals).