The two darlings are so cute as they each divide up the egg, but using different colors and styles for different sections is traditional. I see that Rarity has also included a few five-pointed stars, perhaps a generous yet secret holiday wish to Trixie despite all that happened. (Or *and sing along at home* maybe I'm just reading way too much into it. ) The outside styling is also very peppy and fun.
My only question is whether the dragon who hatches from that egg is going to develop any kind of permanent complex upon seeing her shell.