The sky is orange at night.

This is because of light pollution. In fact, the really pure sky should be blue (this can be explained by junior high school physics knowledge, but it's a long story, so I won't explain it here), but for cities, the air quality is very poor and the concentration of particulate matter in the sky is high, which leads to the impure atmosphere. Yes, the reflectivity is greatly increased. And the lights are very bright at night, and a lot of light shines into the sky, because most of the lights are orange. This causes the sky to turn orange.

Of course, for cloudy days, because there are clouds and the atmospheric reflectivity is higher, it must be orange.