The version I had come across was "all billiard balls have the same color" in Liu's Discrete Mathematics [1]. It is an exercise problem in one of the chapters.

The version I had come across was "all billiard balls have the same color" in Liu's Discrete Mathematics [1]. It is an exercise problem in one of the chapters. [1] https://www.amazon.com/Elements-Discrete-Mathematics-C-Liu/dp/0071005447 https://www.amazon.com/Elements-Discrete-Mathematics-C-Liu/d...