When one says they are at rest relative to the cosmic microwave background, does this mean that they are in a frame where the same frequency is measureed in all directions? Because, I could imagine if I boosted in one direction, then the spectrum behind me would be redshifted, and the spectrum in front of me would be blue shifted. So to be at rest with respect to the CMB I would need to be in the frame where there is no shift in either direction. Is this right? Or do I have it all wrong?