The physical process of scattering causes the sky to appear pink at times and other colors too. During this process, tiny particles of light are bounced off air molecules. Wavelength, time of day and laws of quantum mechanics play key roles in determining the color of the sky.
According to the laws of quantum mechanisms, atoms and molecules only absorb lights of certain colors, such as green and yellow. Other colors, says Double X Science, bounce back into the atmosphere upon reaching the surface of atoms and molecules. The color of reflected light is determined by wavelength, which also signifies energy level. Colors with shorter wavelengths, including blue and violet, have high, intense levels of energy. Other wavelengths, such as those of the colors orange and red, have longer and less intense waves. Upon hitting the surface of other atoms or molecules, wavelengths burst, much like fireworks. Like fireworks, some waves produce brilliant explosions of color: red and pink, for instance, scatter widely upon hitting solid surfaces, and produce magnificent displays of color. After hitting surfaces, the colors released from wavelengths mix and mingle. This explains why the sky turns different colors, and might appear to be rosier one night and more orange the next.