Looking into a clear day with no clouds in the air, we can definitely tell that the sky is blue. What makes actually sky blue is the molecules in the air. These molecules (mainly the nitrogen molecules) scatter blue light from the sun more than they scatter red light.
Then, what makes a red sunset??? According to Legolas, a red sunset means that blood has been spilled during the night. According to science, during sunset we look at the sun at an extreme angle. The sun rays have to pass through a much thicker layer of air to reach our eyes. More blue is scattered in the atmosphere, allowing the reds and yellows to pass straight through to your eyes.