First two are her without her crystal pony texture, second two are with it. I'm intending for her to be somewhat of a counterpart to Twilight, hence the similar colouring conventions (dark grey coat with bright spotting, combined with brightly coloured hair and feathers).
Like the rest of the Mane 6, Sunset eventually becomes an alicorn; in her case, Goddess of the Sun, inherited from the original alicorn of the heavens, Hausōs. In this state, her hair colour darkens somewhat.