Room direction changes natural light quality: north-facing rooms get cooler, indirect light, making colors appear bluish; south-facing rooms have warm sunlight that brightens colors. Knowing this helps you select paint with undertones that counterbalance lighting effects. For instance, choose warmer paints for north-facing rooms to add warmth, and cooler or balanced tones for south-facing rooms to avoid overwhelming brightness. Testing samples in your actual room clarifies these effects before you paint.