...The odd color you got on your coins might be due to toning in the cardboard....
I thank you for your reply, gxseries--and read carefully the thread on the 1974 and related coins (including the excellent info on Soviet-era sets).
I wish I was better at photographing coins, so I could illustrate (what I think is) the odd appearance of these coins. The 50-kopek and 1-rouble are almost unnaturally bright. Which suggests a proof status I know, but it's almost like they had been plated after they were struck. The lower values also have an interesting appearance.
But maybe all this is a function of their intended use as bank exemplars.
I note that Krause offers an "issue price" for these sets; so apparently they
were also offered to collectors?

v.