Which genes at play in this Zebra hen?

[Finchy]

Hi

I have a Zebra hen with markings I've not seen before. She has quite strong black speckling all across her chest and up into the 'white triangle' in front of her teardrops. Her tail is black. Her chest background and back colours are normal. (Sorry, no photo, as too much movement in the holding cage.)

I didn't expect to see these chest markings on a hen. Which mutation is responsible?

Thanks

[Tiaris]

Maybe charcoal?

[finchbreeder]

Without seeing her my best guess would also be charcol. Some of my charcol bred hens show more colour on the chest than those without charcol blood.
LML