Twilight took several deep breaths, steeled herself, turned around, and when she looked up, learned that she should never underestimate her abilities ever again. Stroke by stroke, almost as if with a paintbrush, the moon started turning purple right before her very eyes, the foals too distracted to gasp and scold Twilight for the extremely rude swear word that left her lips as her hoof hit her forehead. She watched as everything surrounding them was tinted a light shade of purple and suddenly got much darker. Oh Celestia…  
-From the fan fic Once in a Purple Moon by Monochromatic  
https://www.fimfiction.net/story/242919/once-in-a-purple-moon