The skin of a polar bear is black, so a shaved polar bear is completely black. The skin has a layer of fat underneath that measures as much as 4.5 inches thick. This fat keeps polar bears warm while swimming since wet fur doesn't insulate well.
Out of the water, the bear's insulating undercoat and hollow hair keep it warm. These three things ensure that, even when the temperature plunges to 30 degree below zero, polar bears lose almost no body heat. Contrasting the black skin, the bear's white fur is actually pigment-free. It reflects the light in much the same way as ice and snow.