The red color of the clouds is due to the fact that the sunlight is scattered by the various components of the atmosphere. On the one hand, the air molecules scatter blue light more than red. This results in the orange color of the sun at sunset. In addition, to create an intense sky-red, however, many water droplets must be in the atmosphere. In addition to water droplets, dust particles (for example from a volcanic eruption) can also contribute to colored twilight phenomena.