Dean really loves dark grey. This is shirt is a gingham-style plaid in grey and charcoal/black. It’s western cut (slightly unusual for Dean) and does up with snaps.
In Various and Sundry Villains (13x12), Dean wears this shirt from when they leave to track down the stolen book until the end of the episode.
In Funeralia (13x19), Dean wears this shirt for the duration of their time in Oregon, except for a brief scene when he and Sam are wearing suits while looking at the crime scene at the art gallery, and then discussing the dead Reaper with Jessica.