The sky is blue due to atmospheric scattering of blue light. Blue photons are the most energetic of the visible light photos, and interact more with the atmosphere as a result. To be clear, all colors get scattered, it s just that blue is affected the most because of it is more energetic.   A related effect happens around sunset. At this time of day, sunlight needs to travel through significantly more air to reach your eyes. The length of air is so long that nearly all the blue and green is scattered away before it reaches you. All that is left is yellows, oranges and reds, some of which reaches your eyes, and the rest scattered in the sky within your view.
Why is the sky blue?