You might like to have a look at this entry in the DT:  :Green Grow the Rushes (Commentary)

Although versions may perhaps have been found in Ireland (along with many other countries, by no means all English-speaking) it is not an Irish song, and a "rebel" explanation for "lily-white boys" is a non-starter.  There have been a number of past discussions besides this one,which can be found in the usual way, and a composite set of the "Red Banners" parody is in the DT, here:

Red Fly the Banners, O

Malcolm