Are you experiencing dryness in your mouth, too?
Is this stain mostly concentrated at the base of the tongue?

Individuals with "black hairy tongue" merely have a taller-than-normal forest of papillae. The extra height comes from an accumulation of keratin, which is the chief protein found in hair and skin. Normally, keratin sloughs continuously and gradually from mucous membranes and skin. (In fact, "discarded" skin cells are the chief constituent of house dust. There is a critter that makes its living by eating this stuff: the dust mite. People who are "allergic to dust" are usually just allergic to dust-mite poop!) In people with black hairy tongue, not enough keratin is sloughed (or, perhaps, too much keratin is being produced at the surface of the tongue).


No one knows for certain what causes black hairy tongue, but there are several well-known associations. ("Association" means, "We see A and B occurring together, but we're not sure whether A causes B.") Black hairy tongue is fairly common among smokers. It is also sometimes seen following treatment with antibiotics. Other associations with black hairy tongue include radiation therapy to the mouth, poor oral hygiene, frequent use of strong mouthwashes and frequent use of antacids.

it is definitely not black hairy tongue. It is over my entire tongue, but I also cough it up in my plegm. My mouth is dry and tastes icky. I do use a lot of antacids.

Marianne0558 has right about frequent use of antacids causing black hairy tongue.
If you are concerned about having black phlegm, you can visit a doctor to get checked for some lung infections.

Are the sides and tip of your tongue involved with this?

it's just on the surface of my tongue. Almost like someone took a majic marker and colored it. nothing on sides or tip. It doesn't seem raised either, like hairy tongue, but I have been coughing more frequently so I think I should get my lungs checked. Thanks for all your comments.

You are welcome!
Waiting for your new informations about checking your lungs!
Wishing you all the best!
Marija