Question

What would be the colour of sky if earth had no atmosphere and why?

Answer 1

Yes. Earth's sky is blue because it's atmosphere scatters sunlight in random directions. If you are looking at a point in the sky that is blue, you are looking at light that originated from the direction of the sun that got bounced around a bunch of times in all different directions until it finally reached your eye.

With no atmosphere, the background sky would be black because all the light from the sun and other sources would follow straight paths to your eye.