No, it's not a pied gene. Yes, pied does exist in green cheeks.
It's a pretty normal feather!
Couple of older threads from a different poster....
http://www.parrotforums.com/conures/29130-my-two-new-conures-one-hybrid.html
http://www.parrotforums.com/conures/27477-yellowsided-but-has-orange-shoulders.html
I think the most interesting thing is is that it's such a bright yellow feather! You don't have a blue green cheek, you have a turquoise... aka par-blue.... aka partially blue. Par-blue mutations are a partial reduction in the psittacin colors (reds/yellows/oranges) but not full reduction as in true blue mutations.
Turquoise green cheeks are often born bluer than what they will appear as adults. As they mature, their blue feathers will turn blue-green. If the feathers are already a blue-green color (turquoise), then they may become a deeper green color, but still blue.
Some breeders are striving to breed the "bluest" turquoise mutation possible, where-as some are trying to work on the "pinkest" turquoise mutation. Other breeders may be breeding with no real goal in mind. As such, you may find varying degrees of the turquoise mutation.
You can see a couple examples of some green turquoise conures on the following page... one is a pineapple turquoise and the other a yellowside turquoise.
Available Babies
And you can see some other examples of the different turquoises in the following pages.
Outback Aviaries
Species we breed - Something Cheeky
So that yellow feather, although odd, really isn't abnormal - per say.
And on a turquoise bird, a pied feather, in theory, should be white. Not really sure!
