I hope you don't mind but I have made a Celestia cursor and am presently using this as a preview image for it. I can find another preview if you would prefer. I have cited you as being the image's source, directly hyperlinking here.
Ugh. I'm doing a vector of Celestia, Luna, the chariot, and the guards from the end of EoH (part 2) for someone. Celestia is just small enough in the frame to be annoyingly low-resolution. Thanks for uploading this vector of Celestia in a nice, neutral pose. I think I'll definitely keep referring back to it to make sure I correctly fill in curves and strokes that I can't see.
Solid colors are easy, if you know what they are supposed to be. Rainbow Dash's colors are easy too, though getting the shapes to all align right is bothersome. Celestia has that problem too, but the G3 Rarity from your link doesn't.
What makes Celestia a real nightmare though are all the gradients (and not just in the fills, but even in the strokes too), and the fact that it's difficult to figure out what her colors actually are.
I tried to use a color guide for her, but apparently her "official" colors are rather different from how she appears in the actual show. So I was left with screenshots, which isn't always the best source for exact colors.