It is a thing of beauty to gaze outside and see red, orange, and yellow hues dancing upon the clouds. It’s been sung in songs, shown in movies, and mentioned in books. It can only be seen at a particular time of the day, during sunrise and sunset. For at these times of the day, the light from the sun has to pass through more of the atmosphere. The warm hues that appears on the clouds occurs from the light being scattered and absorbed from particles in the atmosphere, whether it be gas molecules, aerosols, or water droplets inside a cloud. Since the light ray has longer to travel, it will encounter more particles that will scatter the short wavelength particles away and expose the long wavelength colors of red, orange, and yellow.
This also explains why the sky seems blue during the day. Light from the sun has less to travel, and fewer particles to scatter with smaller molecules composed of our atmosphere. This results in the shorter wavelength colors of blue and violet to appear. Although, human’s eyes are more sensitive to the blue color, so we don’t see the violet.