Nice variation on Rarity's cafe-bohemian look. I can't see her wearing a shirt like that most times, but if she's going to an art gallery and trying to affect bohemian chic I could easily see her wearing that. I also like seeing artists play around with the mane six's physical features and you've certainly done a nice job making Rarity look 'black' and making it work with her purple hair. (Sometimes artists do a good job of drawing her but somehow the hair and skin clash. Maybe it's the hairstyle you've used here.)
((On the other hand it is odd since your human Sweetie Belle is white. Step sisters? Sweetie is adopted?))
i like the idea because i'm pro trying out interesting ideas and designs when it comes to humanized mlp. (its llike ann excersise in character design for me) so the idea of a less cnventional familly is really apppeealing Rarity annd sweetibell semmed ike good choicce snce their relationshipp s more complex and less black and white. Especially when comparing it to aj and applebloom.
Oddly enough I had considered the adopted angle when I saw your Rarity. Somehow I'm inclined to believe that Sweetie is the adopted one, but then I like the idea of Diamond Tiara and Silver Spoon trying to mock her about it...and failing miserably because Sweetie's totally non-angsty about it.
"I know...and I'm so lucky to have a wonderful and loving family to take me in with an awesome sister to boot!"
I certainly regard humanizing ponies as an exercise in character design (and anatomical study) as well. Nearly broke myself trying to give my human Applejack a distinctive set of facial features that I saw her as having, and I still haven't designed the rest of the Mane Six or her family.
i'm working on a picture of the today. Its going to confuse so many bronies lol... and yeahits great that artists are working on making the girls look interested and like real people. though sadly more seem to go for the ideal- dream girl anime big titted monsters...