If you looking to get close to OEM color, try a auto paint store and ask for GM paint code U19. That's a glossy black. But preference on the exact color is in these eyes of the beholder. Great choice of fillers with Goodmarks two piece and Spoolfool one piece, definitely two of the best on the market.
I would also add Gbodyparts to the list. Brian made his off of the original OEM fillers. I bought a set when I had my car painted this year. The ones I got from him are made from fiberglass and the fit is as close to perfect as I have seen even with my limited ability in bodyman skills.