This shirt is hard to see. It does up with snaps and has diagonal plaid along the upper-snap line. It seems to be a very blue plaid when we see it close up, but from slightly further back, it appears more brown and white. There are highlights of red throughout. We finally get a glimpse of it in Red Meat, and it turns out that it is mostly brown plaid, with blue and white being the secondary colours. It’s also a very busy plaid pattern.
In There’s No Place Like Home (10x11), Dean wears this shirt from when he goes to try to protect the salesman from Dark!Charlie, until Charlie’s two halves are reunited.
In The Things They Carried (10x15), this might be the shirt that Dean is wearing in the car while they drive to the case.
In The Devil in the Details (11x10), Dean wears this shirt for the entire episode.
In Red Meat (11x17), we see Dean wearing this shirt during the flashback to the Bunker when Sam found the case.
In The British Invasion (12x17), Dean is wearing this shirt at the beginning of the episode when he and Sam return to the bunker with takeout and find Mick waiting for them.
In Breakdown (13x11), Dean wears this shirt as part of his “trucker” disguise when meeting up with a trucker who saw Donna’s niece the night she disappeared.