Talk:Twilight's Kingdom - Part 2/@comment-3410511-20140627182042/@comment-24908786-20140630153358

I say their manes and tails looked like how they do in the show, even when they still had not gotten their Cutie Marks yet, as told in the Journal of the Two Sisters.

Pure-blooded, natural-born Alicorns age differently, so Celestia and Luna's manes and tails looked like how they do in the show as they were about that same age in the Journal, but had not gained their Cutie Marks yet.

The pink and powder blue manes and tails are probably just fan-inspired ideas from Celestia and Luna's younger years before the events in the Journal of the Two Sisters, by the time that they started their Journal, the Royal Sisters looked like how they do in the show: Celestia's multicolored mane and tail, and Luna's moondust mane and tail.