You have two options, ride up to you local Chevy dealer and but the GM Accessory htich cover in your color Tahoe or, order the Street Scenes hitch cover for the Tahoe online somewhere, then when it arrives have your local dealer paint it to match.
I say just get the GM one, its alot easier of a process. But if your Tahoe is not black/dark colored then you may want the Street Scenes one, looks better or light colors beacause it doesn't have a surrounding weatherstripping!