There were a couple colors in 1971 that were hard to distinguish: GA4 and GB2, winchester gray metallic and glacial blue metallic - given the appearance of the 71 New Yorker in the video above, I would guess it is GA4 given its light gray cast compared to GB2.
Here is the one car that got away from me back in 2010 and it is the one that I regret missing the most of any potential sales over the years and it was also GA4:
I also wonder whether Ken's car, the subject of this thread, was originally GJ4 which was another highly desirable color in 1971 and may have given him the inspiriation to go ever further with his green custom color. GJ4 (April green metallic) is also often hard to distinguish from GF2 (amber sherwood metallic) and are also great colors.