The the Royal Wedding DJ Game: Red Roses and White Lilies... MLP:FiM why are you so awesome?
If you don't understand:
Robert Schuler (“W. B. Yeats: Artist or Alchemist?” Review of English Studies 22:37ff) interprets this last line as relating to Yeats's interest in sexual magic. Schuler also notes that the lily and rose in alchemical literature symbolize the moon and the sun, the white and red tinctures in the alchemical process. More detail can be found in Gorski's Yeats and Alchemy (State University of New York, 1996).