For my Celestia re-design I had to re-think a lot of things.
 
For Celestia, I decided to keep her white coat. With my Luna re-design it makes them look more like sisters. Though, where Luna’s coat glitters in the night, Celestia’s glows with the day.
 
Her cutie mark stays the same, but her coat fades into peach and gold around her fetlocks, and wing feathers. Her mane looks more normal where her rainbow colors have been replaced with hues varying between gold, peach, pink, and pale yellow. Shimmering and mildly floating around her.
 
Celestia is definitely the more vain of the two sisters in my head canon, brought about with her ponies adoration. Her regalia is more regal and flashy compared to her sisters with the addition of sun-pearls, citrine, and amethyst gems. I am sure she would have more than one outfit, though this would be her favorite.
 
Being the extrovert of the two, she loves nothing more than being around her ponies, and making them as happy as possible. Though this slowly leads her to believe she is vastly more important. If Luna had never been banished, over the thousand years she would slowly dive into a goddess like persona.
 
Her colors represent a burnt out soul of whom she once was. But luckily, Solaria never came to pass with Luna’s banishment. Losing her sister leads Celestia to realize her own faults, and instead reigns in her pride to become a better ruler, and hopefully in the future, a better sister.