Hi there. Sorry, but I don’t think your drawing represents the best way to produce a Rubik’s Cube in a 3D modelling program like Rhino (and there is a technical issue with the to-be-black areas - those between the colour blocks should be twice as wide as the ones around the edge).
I’d suggest instead that you make one small cube and then create a 3 x 3 x 3 array of it.
Create a small cube:
Make a small fillet along each edge:
Create a shallow box centred on one face and boolean difference it from the cube (with the DeleteInput option set to No), then give it a suitable colour. Repeat for the other five faces, then group the whole thing:
That should give you the first small cube:
5: Create a 3 x 3 x 3 rectangular array of it to produce the complete Rubik’s Cube: