Question

if atmosphere is not present in our earth what is the color of sky?

Why red color is use in danger signals?
gave the answer it's urgent please
:)

Answer 1

⏺Sky refers to the lowermost layer of troposphere which is visible to us as blue. So if there was no atmosphere, sky would not be there, forget about the colour.
⏺Anyways, if there was no atmosphere, we would be able to see sun and many stars distinctly. Atmosphere acts as "frosted glass" which evenly spreads out sunlight, making it difficult for us to make out sun distinctly. This effect is caused due to Rayleigh scattering of light [more specifically, sunlight].
⏺Space is rather colourless, and so dark. No atmosphere means that there would be space directly after surface. So the so-called colour of an imaginary sky would be transparent black, absolute black.

⏺Red ⭕ has longest wavelength in visible light. It easily travels far away, so it is preferred as a warning sign ⚠ so that people can be warned well in advance.
✔For eg., if somebody is driving a car , and if some construction is going on ahead on the road, a red sign of "CONSTRUCTION AHEAD. GO SLOW" can save them from any accidents.