Gravity, when depicted as an element, tends to be quite tough to visually represent in media, what with it being an invisible force and all. Wind has a similar problem with being colorless, and people from Asia often to depict it as green. What color would they use to represent gravity? As far as East Asian media is concerned, it's often purple. Is it because gravity is powerful? Or maybe mysterious? After all, purple is viewed as a "space" color, despite outer space being mostly black.