Some cause of a green, furry tongue include poor oral hygiene, antibiotic use and radiation treatment. Hairy tongue is a condition in which the tongue develops an abnormal coating, often taking on a hair-like appearance, and turning green, brown, pink, black or white, explains The American Academy of Oral Medicine.
Other causes of hairy tongue include using tobacco and drinking excessive amounts of tea or coffee, notes the American Academy of Oral Medicine. Practicing good oral hygiene and brushing the tongue with a toothbrush or tongue scraper usually resolve cases of hairy tongue. Although the condition is harmless, in rare instances, persistent cases of hairy tongue may require medical or surgical treatments.