The 17th Mississippi began the War wearing a uniform of gray with red trim as prescribed by the ever changing early war Mississippi regulations. Here’s a color version of the Don Troiani image posted above:
However once in Virginia, some companies of the 17th Mississippi wore uniforms of gray with black trim.
According to the diary of Robert A. Moore, a member of the Confederate Guards, camped near Leesburg, Virginia, during August 1861, the 17th Mississippi Infantry purchased 'for the Reg. goods for a uniform' which was taken 'back to the homes of the different companies' to be made up. Received by the end of October, these uniforms consisted of grey ten-button shell jackets with a single small button oneither side of a black trimmed collar. Cuffs were decorated with black cord forming a distinctive single loop. The front and bottom jacket edges were also trimmed with black cord. Some jackets had a single pocket on the right breast. Pants were also grey with two-inch wide seam stripes http://www.angelfire.com/ms2/UniversityGreys/Uniform_summary.html