Poking awake a dying thread I will post the answer to my question and give a new one. The colors of the German flag, black, red, and gold (yes, it usually looks yellow, but it is
supposed to be gold

) go back to the uniforms of the L¸tzow Free Corps, a voluntary unit during the Napoleonic wars. Black uniforms, red seams, golden (brass) buttons. Veterans of the Corps were active in some of the protests calling for a republican government of a unified Germany (most notably the Wartburg Festival and the Hambacher Fest).
Here is the next question. Which (very early) battle in German history is often referred to with the name of the defeated general added with the word "Schlacht" (battle)?