J.C.
I took my oldest who is now 5 to the doctor when she was six months for the exact same thing and she told me not to worry and it was completely normal. She said you can never tell if a baby is cold or warm or even how the circulation is by thier feet or hands. They naturally have poor circulation so thier hands and feet stay pretty cold and blue, some more than others. I would say dont worry about it unless your mothers intuition is telling something is really wrong then it cant hurt the get her checked out by the doc.