My tongue is a whiteish green colour what is this caused by and how do i get rid of it?

Coated tongue: dermatologic conditions are hard to discuss without seeing them. but mostly, this is a coating from sinus congestion, reflux, or something you ate. Solvents (many mouthwashes) will dissolve it.

Maybe okay, but...: 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).