Woman's eye. Thermogram of a close-up view of a woman's eye, showing variations in temperature. The temperature runs from red (warmest) through yellow, green, cyan and blue to mauve (coldest). Thermography is a technique for visualising the temperature of surfaces by recording their emission of long-wavelength infrared radiation. This heat radiation is detected electronically and displayed with different colours representing different temperatures. In this case the surface temperature variations of the eye, skin and hair are shown.