For some time I was working on the idea of a multi-color drawing machine. With this egg-bot, I realized a pen changing mechanism. The model can decorate eggs using 3 different pen colors.
It can write, decorate the egg with repeating patterns or apply self-defined, multi colored drawings to the egg.
Apart from pens, some household rubbers for attaching the pens and an egg, you only need the Mindstorms robot inventor set 51515 – no other extra parts needed.
The instructions are available in English and German on rebrickable.com. All programs are provided as lms-Files which you can directly load into the Mindstorms APP.
Patterns can be customized through the programs menu. For drawings and text, you have to change the python programs as discribed in the instructions.

More Details on the page about the book The Mindstorms Robot Inventor Expert