Yep, the costume was originally some kind of cloth that he left hanging in his locker at work. Sometimes the mask was an energy construct... Sometimes he wore the uniform under his normal clothes and had the ring turn his normal clothes invisible 'revealing the suit'... Alan Scott claimed at least once that he did it the other way around, wearing his 'work clothes' on the outside invisibly... which makes more sense with that giant cape. Sometimes it seems like Hal 'wishing ringed' his uniform on... sometimes not... I really think that was a concept that was the LEAST consistent.
I was never a fan of John's 'Hot/Cold' super suit... but it didn't bother me too much. I really prefer it when their rings run out of charge that they change back to civilian gear though... and not naked. I saw that a few times too..