Formaldehyde turns plantar region of feet red?
It might be due to livor mortis, also called postmortem lividity, which is the settling of the blood in the lower parts of the body which in your case might have been the limbs. By time the color can be interpreted as either blue or purple, but given, that not much time has passed it can very well be the reddish color you might have asked, as stated here on page 39:


  The first manifestation of livor mortis can be expected 20-30 min following the irreversible cardiovascular arrest, initially as bright-red spots that subsequently become confluent and turn bluish-violet.


Which might better describe your case is the fact, that cold conditions can cause bright red color in livor mortis, as it can also be found on page 39:


  Cold conditions, such as keeping a body in cold storage, cause ... bright-red livor mortis.


You can read more about it here or here.

EDIT

I have added references thanks to @Kendall, who provided them.