You never know what sort of toning can affect some of the coins in a Mint Set or even a Proof Set. That particular set has been around for nearly 38 years, and there is no telling what sort of environmental conditions it could have been subjected to. Chris
on a different but the same note. I have a two sets of Susan B Anthony dollars with the same tinting. A 1979 P&D and a 1980 PD&S. Maybe some special mint sets?
Depending upon the storage environment, your coins are gonna tone. The color you mention is toning and has nothing to do with a special process the mint did when the coins were struck.........there was no special process in their production.
I agree with both green18 and cpm9ball above. Most likely the 3 sets were stored in the same environment and therefore will exhibit the same effects of that environment
As an aside, I have an 2005 Westward Journey Coin and Medal Set that has some nice 'yellow' hues showing on the nickles. It's due to the mint packaging.
Some of my rolls of Westward Journey nickels have nice "end roll toning". I think it is caused by the coloring in the Mint wrapper. Chris