just noticed this dumb question.
bigideas, look for clues in the quote. somewhere along the way you never learned that everything you ever need to know is actually right in front of you, at your fingertips, under your nose, staring you in the face. you just hav to trust that you can figure it out, which i doubt you have EVER tried.
ang lee says that he got this information from kubrick's
last costume designer. this means whoever he worked with during Eyes Wide Shut. he also says that he wore this shirt every day.. which means he was quite probably wearing it during the making of eyes wide shut. well what is the FIRST thing you could search for in order to see what he was wearing at the time of EWS?
type "kubrick" into google image search.

this is the official picture released around the making of Eyes Wide Shut. this is most likely the shirt. it's just a normal shirt. it's not "the perfect shirt ever made", it's just his favourite shirt. that's the shirt. mystery over.the inside one or the outside one, does it matter? they are both boring as hell and nothing special. look at PTA and his permanent brown shirt:

he might well say the same thing about this shirt. he loves that thing. he sleeps in it (notice the creases).
it's up to each of us to find our own favourite shirt.