I have been obsessively looking at the 600 and 700 range from the early 80's lately. Other than that, I claim no expertise. I don't know how closely Trek stuck to the catalog specs, but the 82 700's had a color wrap on the head tubes according to the catalog. Also, the 82 700's list the dark blue as having pewter panels, not light blue. For that matter, the 82 600's don't list a blue at all but there is gun metal* listed and a blue bike shown. It also has a pewter panel. Maybe an 81?

*I think of gun metal as gray but the catalog also lists a pewter so I think the gunmetal is blue. I did see gunmetal blue listed as a color in a later catalog.