Wait what.
In Episode 2 Season 1, Luna's hair is well.... hair.
In the latest episode, Luna's hair is all everywhere and misty.
Probably because she has Nightmare Moon inside of her still.
According to Lauren Faust, in "Friendship is Magic, Part 2" Luna basically lost all her magical power. By "Luna Eclipsed" she has fully rested/healed and had her magic back thus the flowing magical mane that is similar to Celestia's.
This is how she explains it, but she noted that since she is no longer in control the team might explain it differently, which opens to many speculations.
Some speculate that she only has that mane during the night when she rules. (like Celestia and Luna switch ruling periods)
Celestia had her magical mane at all periods because she was controlling both day and night until Luna had recovered.
We would need another episode with Luna appearing during the day to figure that bit out, and to find out if her darker colors were night-based or if they are really her permanent look.
and really, Luna became a badass to me when she popped out of the bobbing-apple barrel, scarring a pony, and proceeding to eat an apple.
