I think this coloring page of Mystic is a great one! The dark blue leotard with a gold cape and a crescent moon symbol on her chest give her a powerful and heroic look. Her long black hair and blue eyes make her appear beautiful and mysterious. I would color her cape in a light gold or yellow shade to make it stand out against the dark blue leotard. For the details of her body, I would opt for darker shades of blue and black to give her an aura of mystery. To brighten the image, I would tint the crescent moon symbol on her chest with a light blue to make it stand out. Lastly, I would make sure to add some subtle touches of colors throughout the image to bring it to life.