Go to >System Preferences>Displays>Color> Then go through the monitor calibration process or choose and earlier profile.
I am using the Xrite i1 pro display calibration device and software. FCPX and Quicktime appear ‘correct’ and Motion 4 is displaying under a different gamma setting. Darker/Crushed.
As soon as I reverted to the native Mac profiling in System Preferences away from xrite, both FCPX and Motion match. Bright!
Guess I’ll upgrade to Motion 5 and see if that fixes it.