She says: "Regarding the design itself, the costume's loosely based off a Tang-era fresco. Kind of an in-between outfit, not quite formal enough for high ceremony, but too fussy for casual situations. He should probably have a headdress, but I can't for the life of me fathom what it'll look like." Maybe the headband substitutes?
All my thanks, rasetsunyo. And I love the boat-y Tang shoes as well.