Tortoises, thermogram. Thermogram of tortoises warming themselves on a warm surface. A tortoise is an example of an ectotherm. Ectotherms use their external environment to regulate their body temperature. 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 black (coldest, 17.5 degrees Celsius) through pink, blue, green and yellow to red (warmest, 37.2 degrees Celsius).