According to the Old Dominion University, sunsets get their red color because light is refracted by particles that are in the atmosphere and the red spectrum is the one that is visible. The sky can also have shades of orange, yellow and purple when the sun begins to set.
The different colors in the sky mean the colors with the shortest wavelengths, including blue, have already scattered off in numerous directions and are no longer visible. Orange sunsets appear when the air is most clean and red sunsets occur when the red wavelengths bounce off low-lying clouds.
The composition of the earth’s atmosphere is one factor that will determine what color the sky is when the sun sets. The atmosphere is made of gases and particles, and because it surrounds the earth it affects everything that is visible. Light is an energy that travels in waves and it is part of the electromagnetic spectrum. It also moves in a straight line unless it is interfered with. As the sun sets, the light bumps into the particles that are left in the atmosphere. At first, the lights appears white because it has all of the same colors, but as it bounces off the particles in the air the higher frequencies of lights are absorbed faster and you are left with the lower frequencies of red, orange and yellow.