Hairy tongue (lingua villosa) is a commonly observed condition of defective desquamation of the filiform papillae that results from a variety of precipitating factors.  The condition is most frequently referred to as black hairy tongue (lingua villosa nigra); however, hairy tongue may also appear brown, white, green, pink, or any of a variety of hues depending on the specific etiology and secondary factors (eg, use of colored mouthwashes, breath mints, candies). [2, 3] See the images below:
Handler, Marc Zachary; Butler, David F.; Eisen, Drore; Burgess, Jeff; Lynch, Denis P.; and Stafford, Gary L., "Hairy Tongue" (2017). School of Dentistry Faculty Research and Publications. 253.