I'd go with a black interior. Parts are easily available in this color and if you decide to change the exterior color, the black interior will in most cases be a safe match. That's what I did on my 67. It had a tan colored headliner and interior which was dingy. I used vinyl dye in the spray cans. I dyed the headliner as installed in the car and it turned out great as did all of the other vinyl pieces. I pulled out the seats and used plastic sheeting to protect the rest of the interior and glass. The only thing that I wasn't pleased with was dyeing of the carpet, which was red. It didn't hold up and I would recommend not even bothering with trying it. The cost of new repro carpet is quite reasonable, so I'd just go with carpet of the color that you choose. | 
1966 yellow mustang what color interior would look good? 
