The bright orange and pink clouds in Edvard Munch’s “The Scream” have long been thought to be a product of a volcanic eruption, most likely the very large eruption of Krakatoa in 1883. Volcanic eruptions shoot sulfuric acid droplets and ash high into the atmosphere, producing spectacular sunsets around the world that have been linked to other paintings of the same era. I can remember similar sunsets after the eruption of Mount Pinatubo in 1992.
But today’s blog from the European Geosciences Union suggests that the the clouds in the painting are not volcanic but rare nacreous clouds, which are very high elevation clouds that are iridescent or multi-colored. You can read more about it at http://blogs.egu.eu/geolog/2017/04/26/extraordinary-iridescent-clouds-inspire-munchs-the-scream/. You can also see more examples of nacreous clouds at https://cloudappreciationsociety.org/.