This shirt is a very bright orangey-red. It’s got a strip of blue on the inside of the collar. It does up with black buttons. It’s go a nearly invisible breast pocket as well. Some fans, along with Dean's Red Carhartt, refer to this shirt as Dean's "Murder Shirt", but it's mostly because they confuse the two.
In the Hunter Games (10x10), Dean wears this shirt at the end of the episode when he goes to meet with Claire.
In Inside Man (10x17), Dean wears this shirt the morning after his nightmare, until he goes home from his adventures at the local bar.
In Into the Mystic (11x11), this is possibly the shirt Dean wears while he and Sam dig up a grave and salt and burn a corpse.
In Red Meat (11x17), Dean wears this shirt from when he and Sam go to check out the cabins, until the end of the episode when they’re discharged from the hospital.
In The Raid (12x14), Dean is wearing this shirt when we pick back up with the Winchesters after Mary has left. He wears it for the rest of the episode.
In Beat the Devil (13x21), Dean wears this shirt towards the beginning of the episode when they’re all getting ready for the rescue mission, but then the door fails. He changes out of it after they all agree that they need to capture Lucifer first.