What is 40 shades of green?

"40 Shades of Green" is a traditional Irish folk song that was written by Johnny Cash. The song pays homage to the many different shades of green that can be found in Ireland, hence the title. It was first released in 1961 and has since become a popular tune in the folk music genre. The lyrics describe the beauty of the Irish countryside and the various landscapes and colors that can be found there. The song has been covered by various artists over the years and remains a beloved classic in Irish music.