more info on frostbite injury - from
https://www.webmd.com/first-aid/frostbite
The doctor will collect data in order to classify the injury as
superficial or deep and the prognosis as favorable or poor.
A good prognosis is heralded by intact sensation, normal skin color,
blisters with clear fluid, the ability to deform the skin with
pressure, and the skin becoming pink when thawed.
Blisters with dark fluid, skin turning dark blue when thawed, and an
inability to indent the skin with pressure indicate a poor prognosis.
from