"Rainbow Eucalyptus trees on Maui, Hawaii The phenomenon is caused by patches of bark peeling off at various times and the colors are indicators of age. A newly shed outer bark reveals bright greens which darken over time into blues and purples and then orange and red tones."
Mindanoan gum (or rainbow eucalyptus) found in the Philippines, where the bark is used as a traditional remedy against fatigue. Image by French photographer Cedric Pollet for his book "Bark: An Intimate Look at the World’s Trees." via Brain Pickings.