I like the sound of the green tone interview outfit! I would feel unsure about wearing a t-shirt to an interview as well... you know your area and industry best, but when in doubt for job interviews it's always better to be over- than under-dressed!

I think I am pro-hat overall, though taking it off for the interview itself sounds like a good idea. But maybe they could see you walk in rocking your hat and think "wow, that candidate can really rock a hat!" :)