Good question: I looked into this a long time ago, when I was doing my 68. I'm 99% sure, the insulation I pulled out of my 68 was the original, and it had a greenish tint to it. I replaced it with the same. Then I've seen other originals, like Dave Dodd's car, that are grey. I'm assuming that different vendors, made them different tints. I don't think anyone can call one incorrect, at least for 68's.