Well, the red/white/black were the colors of the German Empire (1871-1918), so 'Dolf used them because he was reacting to the hated Weimar republic's red/GOLD/black. Heh, Hitler was quite the aesthete. O' course, he used the colors in a much more striking and radical way than his predecessors. No matter what your politics, you gotta admit Nazi pagentry looked cool-as-shit.