Mal wears this brown button-down shirt in only three episodes, but it might be the epitome of what Mal would wear (as well as his maroon shirt).
More after the break...
More promo pictures:
Screencaps from Serenity (Pilot):
Screencaps from The Train Job:
Screencaps from Objects in Space:
Screencap from the Extras on the DVD:
Mal wears this shirt with his Browncoat.
My Photobucket Album for Mal.
Serenifly Costumes site for Mal.