As we all know the outside thermometer for the 70's exists in two dial colors, white and black. For years I thought black was for 1970, with white for 71 & newer. Recently someone pointed out to me that the 1972 sales brochure shows the thermometer option with a black dial. Can anyone shed definitive light on which color dial is for what year(s)and please offer the source of that info. I have recently seen two with the GMC logo on them, any clue to the years that was offered on the trucks, or maybe the Sprint (GMC version of the ElCamino)?