A standard 4b is made by somebody that already has money in the pot. Eg. UTG opens and BTN 3b, if UTG then re raises this is a 4b.
A cold 4b is made by someone who doesnt have any money voluntarily invested in the pot. Eg. UTG opens, BTN 3b and then BB 4b's.This would be a cold 4b and in general represents a stronger range than the above spot (although both represent strong ranges).