"If you find a law that states no Negroes can serve in the Confederate army, please post it for my benefit."

The only law that I know of is the conscript law of April 1862 which says white males, but none of the volunteer laws specify a race. The CS army regulations (printed in the Summer of 1861) also say white males, but most of the companies/battalions/regiments were raised by the states using state regulations. Several states allowed blacks to serve in certain capacities. The Confederate government usually accepted these units as organized.