*Pied (harlequin) - can show extremes from nearly white
overall to nearly grey overall with a few white feathers.
More often, head and back are white, crest and throat
yellow, orange cheek patches, upper wing coverts grey,
flight and tail feathers yellow.*
I don't do genetics but I've read and heard a pied is any
mutation that is 2 or more colors. I just love them all and
never bred for color, never switched mates around.
It's funny how terms get changed over the years. Long
ago 'pearls' were called 'lace'.
hope this helps. I just typed in 'what is a harlequin
cockatiel'? in my browser and came up with several sites.