Nice acquisition!
Very clean bike. Dig the Sears style black seat those Rails had too.
If I had to guess on the frame...they needed a purple frame and didn't have one, and had extra green.
I have a friend who recovers Persons banana seats, he tells me crazy stories about taking the originals apart and there is one type of seat UNDER the other, like a Schwinn Orange Krate seat under another cover, etc. Probably the same principle here, need a purple frame fast...paint a green one.