+1 on what Laitch says about the paint matching, even IF someone can mix paint to the original code, I can almost guarantee that it won't match due to age/UV/sun exposure fading....
As far as the fixing the dent, I understand wanting something to look nice. Lets be real here. It's a 35yr old bike, and unless you are going to do a full frame off restoration/powder-coat of the whole bike just fixing a dent in the fuel tank isn't going to improve any resale value(or insurance settlement from an accident)......
Not trying to be a downer, just stating my opinion. BTDT. I have a 6" crack in my LT fairing from a drop. Could I have it fixed, yes for a price. To me, it's not worth it and it doesn't hinder my riding it.