Simple Green soaking of black seat belts???

I just used dish washing soap and hot water, stir, rinse and repeat a couple times. came out great. for the plastic buckles i used black vinyl dye from part store but when i sprayed it, it seemed to go on a bit thick and cover some of the grain pattern, so i found a lint free rag and sprayed the dye on it and just rubbed it on, THIS WORKED GREAT.