I also have for many years thought that a Whiteface Green mutation was entirely feasible. I did, actually write of the possibility of a future Whiteface Green in correspondence with Clive Hesford, our vice-president, a few years ago. He may recall the circumstances. The common White-face Blue mutation and the double factor version of Yellowface Blue Mutant 1 suppress the yellow completely, giving us a bird with a blue body and white head and mask. I find that it helps.
Allies work together, and so do alleles.
It seems to me to be entirely logical that this should happen. All Blue series birds, whether they be Yellowface, Goldenface or Whiteface, are recessive to Green, so a visually Green bird can be split for Yellowface Blue Mutant 1, Yellowface Blue Mutant 2, or Goldenface Blue, in exactly the same way as it can be for ordinary Whiteface Blue. A Blue bird of any of the mutations mentioned, when bred with another Blue bird of the same or any other Blue mutation will produce a Blue result, whether it be Yellowface, Goldenface or Whiteface. A Whiteface Green mutation will make the series even more interesting. Anyway, thanks very much Margaret for your thoughts on the subject.