'"Forty Shades of Green" is a well known song about Ireland. It was written by Johnny Cash in 1959 while on a trip to Ireland.[1] Contrary to popular belief, Cash did not invent the term 'forty shades of green', it had been used in Ireland many years before he wrote the song.
He released it as a B-side of The Rebel-Johnny Yuma released in 1961. It is also featured on two albums: 1. Ring of Fire: The Best of Johnny Cash, released on Columbia Records in 1963 and 2. Johnny Cash: The Great Lost Performance - Live at the Paramount Theatre, Asbury Park, New Jersey recorded live in 1990 and released in 2007.'

That may be the source of the confusion.