Quite often, particularly in more modern songs, the color is picked to rhyme. And often, probably due to a Puritain influence, bright colors are associated with sin.

To quote the notes in "The Long Harve3st: (Ewan MacColl/Peggy Seeger),
"... GREEN seems to.mean something. Occasionally the lady herself is 'drest in green'. This insistence on this colour, kept so clearly in meaning when it could easily have gone the way of many of the refrains (which often degenerate into hilarious parodies of themselves during oral transmission), is not accidental. Green is the colour of death. Fairies and witches like this colour, and ghosts often dress in it. Even now, it is not the colour for brides or new-born babies (Anne Gilchrist suggests 'it had reference originally to a fear of incurring the hostility of the spirits of the woods by borrowing their livery'. JFS VI, pp. 82-84). To dream of pulling green heathergreen apples, green birk (i.e., the untimely end, unripened fruit or plant)
is a premonition of death. Green is the hue of poisons, of envy and
iealousy This consciousness of the malevolent nature of green is sunk so deep in modern-day consciousness that in Britain a green second-hand car must be sold for 10 per cent less than a similar car of another colour."

(I don't know how that jibes with British Racing Green, but I simply quote)