We start with the fact that sunlight is made up of the colors of the rainbow. Each color has a different wavelength, with red being the longest waves and violet being the shortest. As sunlight passes through the atmosphere, it hits atoms of nitrogen and oxygen, as well as water molecules, dust, smoke particles, and all sorts of other tiny particles. Most of the longer waves (red, orange, and yellow) pass through with very little scattering. Many of the shorter waves, especially blue, are scattered. That scattering makes the sky look blue.

Now, look at the paragraph above. Imagine that the words are the atoms and particles that scatter the blue light. At noon, imagine the light moving straight down from top to bottom. There are only a few lines of words, so less of the light is scattered. The light that reaches us still has a fairly full spectrum.

At sunrise and sunset, imagine the light moving from the top, left corner of the paragraph to the bottom, right corner. It would hit a lot more words (particles) so much more blue light would be scattered and removed. That would leave the long red, orange, and yellow waves to give the sunrise or sunset its spectacular colors.