The sky appears blue because some of the blue components of the sunlight are scattered by:

When the sunlight enters the earth’s atmosphere it gets scattered due to air and gas molecules present in the atmosphere. Sunlight is made up of seven lights, where a few colors have longer wavelengths like red and orange, and others have shorter wavelengths like blue and violet. But lights with shorter wavelengths get scattered the most because of the air molecules, so blue gets scattered the most, and colours like red do not get scattered. Wherever we look, blue light falls on our eyes after getting scattered from the atmosphere, so we feel the sky’s colours as blue.