This plaid is interesting, because the white in it isn’t exactly white – it’s more the effect of having the plaid washed out in stripes. Other than that, it’s gold and blue with white snaps.
Sam first wears it in My Heart Will Go On (6x17), when he and Dean try to save the lawyer from death at the hands of Fate (and are unsuccessful). He keeps it on for the rest of the episode.
In Southern Comfort (8x06), we see Sam wearing this shirt during a flashback to when he returned to Amelia’s after she had kicked him out to tell her that he didn’t pity her..
In As Time Goes By (8x12), Sam puts this shirt on after Henry disappears to “fix everything”, he wears it until the end of the episode.
In The Great Escapist (8x21), fake!Sam wears this shirt at the beginning of the episode.
In Sharp Teeth (9x12), Sam wears this shirt when he and Dean our on their little stake out at Garth’s in-laws house. He wears it until the evil werewolves are killed.
In Book of the Damned (10x18), Sam wears this shirt at the end of the episode when he’s back at the Bunker, and also to the flash- forward to when he speaks with Rowena.
In The Werther Project (10x19), the episode opens with the flash-forward from 10x18, and Sam is still wearing this shirt while he talks to Rowena. He keeps it on as he travels to Tulsa to meet up with Dean, and then goes back to the Bunker to start researching where the Codex might be.