Hey Caveman. You've got the kit that does the '80 Monte, haven't you? The colours for that car, I expect would be:
bodyshell - white
striping - light blue, blue, royal blue
I dug out an old issue of Scale Auto Modeller which had a build in it, & the writer mentions he had a problem with the fit of the darker decals, so he mixed up satin black/french blue to blend them in. That would indicate the darkest of the 3 colours is darker than royal blue. In any case, the main bodyshell is white. Matt black interior.
HTH