I would almost bet that it was the 33rd Arkansas' colors. They got pretty chewed up at Jenkins Ferry, with the highest casualty rate of any Confederate unit engaged there. With the generally poor visibilty on that field from the black-powder smoke mixing with the rain, it would not be too hard to believe that when the color-bearer went down nobody noticed where the colors were. That would preclude the classic CW scenario of some soldiers "rallying around" and supporting the colors. From there some Wisconsin unit could have taken them.