My car is numbers matching with original color paint and interior.
That being said: I wouldn't mind having one that wasn't.
I've owned it for about 16 years now and love it. When I restored it I was careful to maintain the integrity of it's originality for the most part. Fortunately it is Aleutian blue with matching teal interior, and blue has always been my favorite color. I did leave the vinyl top off when I re-did the car though thinking that it is easily enough added if I ever change my mind. But if the original color combination were something that I wasn't crazy about I would have had no problem changing it.
That makes some people cringe, and while I understand their point, I don't necessarily agree with it.
My feeling is that I bought and restored the car for me to enjoy, not for the next owner. I'm not in the classic car business and never viewed my GTO as an investment. My intention is to never sell it unless something really critical comes up where I need the money desperately. At almost 60 years old now, that is less likely to happen than it was when I was much younger and less established.
The reality is that my kids will most likely be the ones to sell it if and when the time comes, and getting a free 68 GTO to do with as they wish is a pretty good deal for most people, and I doubt they'd be too concerned about 100% originality. That's why I just upgraded to the ram air manifolds and a 2 1/2 " mandrel bent exhaust system, and am setting my sights on a disc brake conversion for the Spring.
I say paint the car whatever color you like and enjoy it. There were a lot of great choices in 68, and just about every one of them go well with a black top and interior.
If the black interior gets too hot for the Arizona sun, then change that too if you like.