Hey Choptop,
As Marv said above that is the best way to determine original color and trim colors. But you might be able to determine that if you look under the dash area and see what color that is as many times when a car was repainted in the past that area did not get painted. Of course if it underwent a complete rotisseri style restoration that might not work. Another simple way is to look at the chassis rails where the infamous healey rust protection covered everything up over the years - that being the oil leaks ! Again, unless car has had a rotisseri resto chances are the frames rails are original. And if someone sprayed everthing underneath with some kind of undercoating, usually those oily frame rails did not get covered or if they did, usually can remove the undercoat and see original color. But absolute best way is the certificate.
Regards,
Mike