Female Chinese painted quail, US Red-breasted changing to male coloration

Another very interesting young female bird, born in my aviaries in 2021.
Firstly grown with normal coloration until adulthood this female has progressively changed to a male coloration.
Those pictures clearly show us the apparition of the typical “blue” male feathers and the bib drawing on remaining female background colors.

Because this rare phenomenon tends to be repeated on a very regular basis in my breeding for at least three years, I am busy looking for an explanation for it.