I would color Cinderella's old dress with light blues and whites, making sure to shade in the tattered areas for an aged effect. The new dress could be given a fresh, magical feel with a glimmering white fabric complemented with a glistening blue sash. Provide variations in the blues and whites to give the dress depth and sparkle. Make sure to make the skirts of both dresses stand out with more vivid colors like pale blue and silver. Lastly, I suggest giving Cinderella's bare feet a rosy hue to complete the search for a happily ever after.