It’s another “mystery game” today!
Quadromania XL appears to have originated as a type-in listing for a German Atari magazine, but beyond that there doesn’t seem to be a lot of information out there online aside from the name of its creator — one T Meyer — and the person in charge of Loesungsalgorithmus (“solution algorithm”, apparently), A Blohm.
It’s a simple but enjoyable puzzler based on a straightforward concept: pick a block to swap the colour of, and all the blocks surrounding it will also swap colours. Repeat until the whole screen is one colour or you run out of moves. Easy, right?