Here's why:

* Scattering of sunlight: The blue color of the daytime sky is caused by a phenomenon called Rayleigh scattering. Sunlight is scattered by particles in the atmosphere, and blue light is scattered more than other colors.

* No sunlight at night: At night, the sun is below the horizon, and there is no direct sunlight reaching the Earth's atmosphere.

* Stars and moonlight: Instead of scattered sunlight, we see the stars and the moon at night. The moon reflects sunlight, and the stars emit their own light.

So, while the sky might appear black or a very dark blue at night, it's not the same blue as the daytime sky.