Mucosal melanotic maculehttps://en.wikipedia.org/wiki/Oral_pigmentation#Melanotic_macule
Mucosal melanotic macule can be found on the oral mucosa, lip, palate, and gingiva. Mucosal melanotic macule are benign pigmented lesions that are found in the oral cavity, caused by an increase in pigmentation of the epithelium and the lamina propria. Clinically presentation is typically a brown, black, blue or grey area that is well circumscribed, lesions are usually less than 10 mm in diameter but can be larger in some cases. It is a benign disease.

Diagnosis and Treatment
Mostly benign if uniform in shape and color.