In 'How to Restore Your Mustang' by Larry Dobbs and Donald Farr, there are exterior color patch samples. That might be a place to start. Over the years, owners repainting their cars get an 'almost' the same or get a slightly different mix due to the changes in paint technology and government regulations. There are three 'almost' 65 colors, Honey Gold, Beige Mist and Antique Bronze, that it may be. I assume that the door data tag is not available so if it's supposed to be original, inside the trunk or under the door scuff plates would be the place to look.
Jim