Hatched 7 babies out of my Black Cheek male/Gray female not too long ago, and one's significantly lighter than the others. Not only is it diluted in plumage and beak color, but it's always fluffy. Constantly puffed up (except when upset), whereas the others aren't. Could it be a Fawn? 
If not, please forgive sore lack of knowledge. Finches aren't my forte.
These are the parents:
~Alex

If not, please forgive sore lack of knowledge. Finches aren't my forte.

These are the parents:
~Alex