I neglected to mention that this song appears to be a variant of The Cruel Brother (Child #11), with a more complicated refrain and a happy ending!  Child's versions E, F, G, I, J, K, L & M all contain the three suitors dressed in different colours; version G also has the Fine flowers i' the valley/ Wi' the red, green , and the yellow interlaced refrain.  Baring Gould, of course, had noticed this connection and mentions it in his notes.

Malcolm