Preface
This is a recreational problem I kinda figured out during my free time playing around with the Rubik cube, so I hope everyone will take it as chilling as I did.
Okay, so for those of you who are yet familiar with the notation of movements in a $3\times3\times3$ cube, here's the reference: 
I mean it's easy to remember: just the initial of Up, Down, Left, Right, Front, and Back for the clockwise movement and add the apostrophe to the counterclockwise movement.
Now on one beautiful day, I suddenly hate solving the cube normally and searched for different configurations, and I stumbled upon this problem:
What is the optimal way to bring the cube to the state where no two adjacent square shares the same color? $\tag{1}$
Now apparently one of the ways is to do $UU-DD-RR-LL-BB-FF$ and you get something like a 3D-checkerboard.
But now what if I require more delicacy than that, say: at least 3 colors per face?
I mean that's totally possible: I do $U-D'-R-L'-U-D'-R-L'$and yes! We get this very beautiful cube:
Now if you notice, what I did was I randomly move with $U-D', R-L'$and you can also add $B-F'$ if you want.
My conjecture is, for the optimal move (which I mean you don't do U-U' continuously). Then for any scheme as described in $(1)$, the only optimal way to achieve it would be to rotate opposite faces of the Rubik in opposite directions.
What do you think? Can it be proven or not?