Inara wears this dress in The Message. It has a corset bodice with a skirt of the same material.
More after the break...
More screencaps from The Message:
A signed photo of the cast, with Inara in the dress, where you can really see the front slit with the contrasting material:
A Behind the Scenes shot:
My Photobucket Album for Inara.
Serenifly Costumes site for Inara.