I was inspired by this piece >>2353575 for the mane and @/Earthsong9405 's design for twilight, mainly the wings.
I don't really have a problem with the canon older Twilight design, but it could have been explored a bit more. I guess the only thing that bothered me was that they used Celestia's model for her body and face, everything else was fine.
So anyway, I headcanon that since she's in charge of the sun AND the moon, that would reflect in her wings and mane, specifically in the colors, cause y'know, lots and lots of magic = pretty pony designs :3 I also have this headcanon that a unicorn's horn gets a gradient of color as they keep using their magic.
Also mentioned here: >>2297473 The gradient's the same color as the user's magic