Every scene has its own neutral tone, the average warmth or coolness of its light. Some areas fall warmer than that neutral: sunlit surfaces, skin in golden light, firelight. Others fall cooler: shadows, overcast sky, reflected light from a blue wall. Painters use this warm-cool contrast deliberately to create depth and atmosphere. This tool reveals that contrast visually. Areas warmer than the scene's own neutral glow orange; areas cooler than neutral glow blue. The stronger the shift, the more saturated the color.