Is the boat painted bright orange or is it the original gel coat colour? If it's painted, you might be able to get a flake of paint off to get an exact match (although the chances are that over the years it will have faded) and if it's the gel colour (and the maker's still in existance) you might be able to get a reference colour from them. Final option as a respray of the whole hull in a colour that's as close as they can find to the original.