This phenomenon is due to the process known as Mie scattering, one which is responsible for the white colour of the clouds at daytime.
At one point, theory suggests that clouds appear red at sunset because of the earth’s pollutants. The red colour of the clouds is a reflection of the sun’s beam of light striking the polluted atmosphere of the earth. This reflection comes from the smoke, smog and other gases emitted from factories, vehicles, and so on that are hit by the sun’s radiant beam of light. On the other hand, the phenomenon could also be explained by the idea of wavelength. Particles in the atmosphere like oxygen and nitrogen can scatter violet and blue light from the sun due to their size. Thus, the more we are closer to the sun, the more we would see sky as blue during day time. However, at sunset, considering that there must have been too much blue and violet light that has been scattered for the day, allowing the observer to see light of longer wavelength, clouds may substantially appear red. This is called Rayleigh scattering.
The Green Flash seen in sunsets in Hawaii is one of the most spectacular events in the place. This is due to light refracting in the atmosphere. At sunset, the different colours of light rays from the sun are refracted at the atmosphere. The refraction provides varying colours that may overlap each other. At some point, the green one may overlap the other in a flash, which is a brief and sudden phenomenon. That is why it is called a green