Do you mean its faded? I havn't had the pleasure of seeing the interior of a new mustang, but if its plastic coverd you can get a can of spray interior dye the same color and spray it on and it will be good as new. If its not faded to get a replacement look in a salvage yard or your local ford dealer. Or you could just buy a trick billett LED 3rd brake light and replace it.
HK
HK