For my Luna re-design I wanted to portray her connection to the moon in her color scheme.
I have taken your dark princess and she is now glittery white with night sky accents. Her cutie mark is a full moon. I have given her extra long white hair that blends down to a night sky. Her regalia is made from black obsidian and blue pearl with different moon phases. Her wings are a mix of both feathers and bat-winged.

My headcanon Luna is an extreme introvert. Which is why taking care of the night and dreams by herself don’t actually bother her. She would rather Celestia take care of dealing with ponies during the day.

What happens though, since she is rarely seen in public, and is mostly active at night that ponies still end up fearing her. She would look a lot like a ghost at night. So sadly, numerous rumors get started, and ponies end up having nightmares about her, which she has to witness while caring for dreams.

She tries bringing this up to Celestia, who ignores her, and tells her she shouldn’t care about rumors that are false.

Eventually hurt and angry, she turns into "Blood Moon". Blood Moon doesn’t care about love or devotion. If ponies wanted a monster to fear, then she would give them something to be afraid of. She appears as a dark specter with blood red markings that terrorizes ponies while refusing to lower her moon, and coloring it a deep red.

Celestia ends up having to banish her younger sister to the moon with the elements of harmony to save her little ponies from any more terror. During her thousand year banishment she is only remembered as a old ghost story that no pony actually believes in any longer.

And that, is my Luna re-design! Let me know what you think. =)