Enough said. Thank you, mister commissioner. Just thank you.
The Celestia mane outline fadeout is a fine idea for showing its ethereal quality. And I really like what you did for their shapes and their expressions here. Twi's chin seems to be a bit on the thick side to me, but it's fine, 'cause you managed a really, really awesome Celestia head. Well done!
A little bit, yes. Two separate colors (the ponies) existing in a shared space through unifying elements (the color of the highlight and shadows.) There's some nice stuff in here [link] on how any two colors *can* go together as long as they're properly separated but also unified. Separate colors are like two chemicals that can't mix till you put them both in water.