I think you are thinking of the song "Green Grow the Lilacs" originally "Green Grows the Laurel" an Irish song. The song title is familiar as the source of a dubious popular etymology for the word gringo, supposedly being a Hispanicization of "green grow", which Mexicans certainly could have heard U.S. troops singing during the Mexican-American War.

The cowboys in south Texas loved to sing the song. Across the way, Mexicans, who could not understand the words, could only hear "green grow". So white Americans became known as "Gringo" by the Mexicans.


          Green grow the lilacs, all sparkling with dew
          I'm lonely, my darling, since parting with you;
          But by next meeting I'll hope to provre true
          And change the green lilacs to the Red, White and Blue.

          I once had a sweetheart, but now I have none
          She's gone and she's left me, I care not for one
          Since she's gone and left me, contented I'll be.
          For she loves another one better than me.

(There are other versions)