Today I received the 330Ohm-resistors and bright blue LEDs I ordered. Each LED now has its own resistor, which makes all of them equally bright all the time.
So now I removed the old LEDs, replaced them with new ones, and moved them to the board to be on a straighter line. Now the LEDs are connected so that I don’t need the mirror()-function anymore. That makes the program faster and more synchronized. I also changed a bit the led()-function as I noticed that every led()-function was followed by a wait()-function and implemented some more characters.
Here are some new pictures and the new code: