Bob and Sandee, fiberglass has it's finish applied in the mold. Actually, the finish layer, called the gel coat, that you see is the first layer that is applied and the strengthening layers are applied over that. When you remove the finish layer, there is no really great way to replace it.
Another point is that a few years ago, there were some posts here from a gal that worked in a factory that made the shower enclosures. She said that they had over 40 different mixtures that they used for the color white. Different manufacturers or wholesalers would request slightly different gelcoat colors.
Since you have removed the gelcoat, or scratched it badly, you will have to look at replacing it. You should look for an industrial fiberglass supply store, a boat repair yard or a boat repair and fitting store. Without knowing what you have available, it's difficult to comment further, but one of those places should be able to offer some local guidance. There are a few hardware stores that have some pretty knowledgeable people in this, but most of them are smart enough not to try. I don't recall seeing good fiberglass polishes and cleaners, let alone gelcoat and dyes, in home centers either. They are pretty specialized products. Boat hulls have been the most common big, shiny fiberglass parts for years though.