The color of the teeth
is either because of intrinsic stains or because of extrinsic stains. If your teeth were with normal color earlier and now they turned brown. Then it's extrinsic stains and can be removed with cleaning and scaling by the dentist.
If the stains are intrinsic, or due to fluorosis, it will not go off by scaling, then it requires other treatment like veneers
. Please share the history and your photographs for further evaluation.