Liberty cotton, if that gives you an indication of how highly I consider the quality of the pattern :) Several of the Glenjade colorways would be lovely.
Oh, speaking of fabric! This is Marc Jacobs shirting from Mood Fabrics (no longer available). It's light and pretty and the print is a little retro. I bought it to make an unspecified top a while ago, but since it was pretty inexpensive ($15 for 1.5 yards), I used for this wearable muslin here. Which reminds me--I made the top (with a second set of cuffs) in 1.5 yards, so that's good to know when I'm shelling out the big $/yard.
Here's how I wore it, with a bright orange sweater (from Anthro, a few years ago), cuffed-up jeans and maryjanes. And here is where I start to see the utility of collared, cuffed and button down shirts!