Melanosis , increased pigmentation. May be of several reasons...from very long time or naturally if your body colour is darker means its hereditary , it cannot be changed . If uneven tone may be solar induced, hormonal changes, nutritional (decreased vitb12, ferritin , vitb12 level). Kindly check the fastinging level of all this with routine blood investigations. Chemical peels, Q-switched lasers,  glutathione oral supplements topical non-steriodal skin lightening agents like glycolic , vitC..etc may help.