Two observations- First, wood shingles get the weathered look REALLY fast, so it is quite possible that they just changed colored that quickly.

Second, to me it seems like the RGS usually used what was laying around to repair things. It is entirely possible that the shingles were in a pile somewhere, and were used because nobody had to write a check for building materials. I'm sure many (most?) buildings, water tanks, etc on the RGS were roofed with the stuff, so it would make sense there were bundles of shakes laying around back of some shed somewhere, perhaps dating back decades before actual use.