These are all beautiful! I love this series; I really should keep a +Watch on you.
This one's my favorite so far, too; it seems to be the sunniest and brightest and most colorful, and the garden that Luna's finding herself in here is just beautiful. The armillary sphere is a lovely touch, and I really like how the garden, despite being so obviously well-tended, appears to be entirely empty save for Luna (and maybe Celestia) -- there is something very peaceful about that, really making a place to retreat to when you need to escape from the day's cares and perplexities and your royal duties for a while to recharge for a little bit.
I'd been considering posting them combined in some sort of collage, but couldn't decide on the arrangement and how many together. So I just posted them as separate images. There'll probably be more to come, but I'll think about making one or more collages when the project is finished.