What are the risk factors for getting yellow tongue?

Maybe thrush(fungus): The tongue is known to have many variations with pigmenting, size, appearance, & not always due to disease. Causes of tongue that looks patchy 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).