When the sun is at its highest point in the sky, light travels through the least amount of atmosphere, allowing short wavelengths of blue light to pass through. Clouds effectively reflect light waves, which is why the sky appears pink when clouds are present. Blue light from the sun passes through more of the atmosphere when there are clouds above it, so less makes it to the ground. The effect can also be seen during a sunset or sunrise when the sky turns pinkish-red. Here too, clouds block out most of the sunlight, leaving only a small fraction to reach the ground. The color difference between clear and cloudy skies depends on the type of cloud that's present. During a sunset or sunrise, the color change typically ranges from pale yellow for thin clouds over a white surface to an intense red for full clouds over a black one. But the effect is not visible from every angle; it depends on the orientation of the viewer with respect to the sun. For example, a person facing east would not see the color change from a rising moon. That's because the moon is not blocking out any light from the sun; instead, it's reflecting some of the sun's light back toward Earth. In conclusion, pink clouds mean that you're seeing light get filtered by particles in the air, just like glass filters out certain colors of light.