This shirt appears to be black with very subtle stripes. It does up with snaps and has a western-cut, like Sam’s other shirts. The snaps are black ringed with silver.
In Abandon All Hope (5x10), this is the shirt Sam wears during the symbolic Hunter’s funeral for Ellen and Jo.
The shirt makes its reappearance in Pac-Man Fever (8x20). Sam wears it when Charlie arrives and, except for a brief scene by the second body when Sam wears a suit, keeps it on until after Charlie leaves to go get pie and doesn’t return.
In Family Feud (12x13), this might be the shirt that Sam is wears at the very end of the episode when Mary returns to the Bunker and confesses that she’s been working with the Brits.
In The Raid (12x14), Sam is still wearing this shirt as Mary and Dean continue to argue. He changes after Mary leaves.
In The Future (12x19), Sam wears this shirt for the entire episode.
In Wayward Sisters (13x10), Sam is still wearing this shirt the entire time he is in the Bad Place. He only changes out of it once he and Dean are rescued and have access to their stuff again.