Bottlenose dolphin (Tursiops truncatus) calling, thermogram. A thermogram shows variation in temperature on the surface of an object, measured by the long-wave infrared radiation it emits. The temperature scale is colour-coded and runs from purple (8.4 degrees Celsius, coldest) through blue, green and yellow to light red (warmest, 26.2 degrees Celsius). Most aquatic mammals have an insulating layer of blubber beneath their skin.