Since the sixteenth century, when German peasants waved it to wish the end of social injustices, the rainbow flag has been a symbol of hope and social change. In the last century, it has been used in Italy by the pacifist movement, in South Africa by the anti-apartheid movement, and worldwide to support the reasons for collaboration and the rights of the LGBT community. For scientists, however, the rainbow is an optical-atmospheric phenomenon that occurs when sunlight passes through the drops of water suspended in the air after a storm. Since Newton's time, the rainbow was thought to contain every color, but that's not true. The next time you look at one, look for poppy red (you won't find it).