Rubik 3x3x3 Void Cube (a.k.a. Holey Cube)" - Copyright J. A. Storer
Whenever I'm trying to solve the middle layer of rubik cube, just when there is one piece left on each side, there are no parts left without yellow I always come across
Rubik's Cube | The Official Centreless 3x3 Rubik's Void Cube, Difficult Colour-Matching Puzzle Toy : Amazon.co.uk: Toys & Games
permutations - Can a shuffled Rubik's cube have 2 faces with the same number of pieces of the same color? - Mathematics Stack Exchange