It's some kind of teal cotton with a white floral pattern--the regularity of the pattern detracts somewhat from the circularity of the skirt, though it's a nice pattern in principle.
The skirt ties in the back with a white ribbon, to match the white flowers.
It's a cute, simple design from the front, and would look nice with a lacy blouse if I ever manage to make one... the poor Pullip is half naked in most of these shots. :C
Unfortunately this makes the skirt mostly unwearable. It's all right when Eun-Jae is sitting down--actually, it's quite convenient in that case. But really, how much time does a time-traveling secret agent spend seated? It's not very exciting.
In this shot you can also see my poor bow-tying effort and my failure to iron the skirt fabric perfectly flat.
Here's a link to a tutorial for my (and your?) future reference.
Awkward skirt element: the split in the back tends to sit open. This could have been fixed by making one side longer (without sewing the ribbon to the extra length) and slipping it underneath. In the meantime, I suppose I've found a use for the Pullip boxers!