My buffs feet look like this and this does not look like frostbite to me.
We had a sultan rooster (had to put down yesterday) that had SEVERE frostbite on both his feet. You would see absolute black on the feet...just like humans....the flesh is dead. We nursed our sultan with epson salt lukewarm bath for the feet and tried to get the circulation going again by massaging feet. We then put antibiotic cream on the feet so as not to get infection if any area was open wound. We nursed our roo for four weeks with same routine and unfortunately two days ago we picked him up...feet were swollen to the dead toes...and he had a hole (which looked like he had ripped it with his nails) in his breast part. We called our awesome vet and he directed us to bring him in. We found out that he was fighting an infection (probably gangrene setting) and that is why he would not heal. We were advised to put him down. We brought him home and we are going to bury him.
Some of the things you will see if it is severe frostbite is the chicken will not be able to walk on feet. Out sultan "Buddy" would walk on his legs not feet (so as to drag himself) and so he was creating abrasions on his legs which we put antibiotic cream on.
FYI: feathered feet chickens need extra care in winter. You will need to make sure their feet are dry so as not to create moisture to freeze their feet.
Most other chicken breeds should weather fine. This is my first year with feathered feet and learning alot. Seems like my roos are more susceptible to get sick. I lost another sultan roo beginning of January. He had respiratory issues. I have not had a problem with my others and frostbite.