Electorate of Hesse – Flag in Lexicon and Shop https://www.flaggenlexikon.de/fdtkhess_me.htm
The Landgraviate of Hesse-Kassel was elevated to the Electorate of Hesse in 1803, and in 1868 it was annexed to the Prussian province of Hesse-Nassau. Its flag showed the colors red and white.
It was a three striped bicolore, with three stripes