Information from artist in the original post:

• Celestia
— "sick" version: Albinism. She has almost white colors, very sensitive skin to sunlight and weak health. Yes, she is princess of Sun but she cannot being under sunbeans a long time. Also her hair half dragging on the ground. Because her magic is weak due to albinism, which makes her very vulnerable to sun and her own solar magic.
— "healthy" version: Symbolic albinism or Leucism. She has normal health and magic power, not vulnerable to sun. She is just kinda dazzlingly light like sunlight and her colors are pale like they have faded under Sun. Her exterior is symbolic and reference to belonging to the day luminary. Hair spreads on the ground just like aesthetics.