Christine wears this costume during Il Muto in her part as the Pageboy, or the "Silent role." In the middle of the performance, she removes the hat and skirt, as well assome of the bodice to reveal that she is not a maid, as the Countess's husband thinks, but the Countess' secret lover.
Bodice: I'm currently reseraching historical references, so not much yet.
Images: Most of the images below are hi-res, so they may take a bit to load, but trust me, they're well worth it!
Ebay Auction:
Bodice and Shirt
Unfortunately, there isn't much to tell because of the lack of good pictures, but here is what we know so far.
The bodice is made of a light green, yellow, red, and blue striped fabric.