Magic wasn’t that well planned out in the beginning,
the first episode didn’t even have a blow around objects. [S1E1]
The third episode gave the objects a yellow glow. [S1E3]
But it was quickly changed so Twilight had pink magic,[S1E4] and Rarity light blue,[S1E6]
but it was very inconsistent [S1E5] and they sometimes switched it around. [S1E8]
It wasn’t until the true start of season 2 (episode 3, that is) that they gained the more prominent magic design;[S2E3] and Twilight and Rarity kept their own colours much better.
The only reasonable explanation for her behaviours
the first episode didn’t even have a blow around objects. [S1E1]
The third episode gave the objects a yellow glow. [S1E3]
But it was quickly changed so Twilight had pink magic,[S1E4] and Rarity light blue,[S1E6]
but it was very inconsistent [S1E5] and they sometimes switched it around. [S1E8]
It wasn’t until the true start of season 2 (episode 3, that is) that they gained the more prominent magic design;[S2E3] and Twilight and Rarity kept their own colours much better.