I have the same issue with a RED ESC ... One side seems much brighter than the other... I had to recently replace one RED ESC's after a crash, and now that's the side that seems to be brighter... It doesn't seem to matter though... My Phantom flies smooth and flawlessly... You can see the differences at the 1:25sec mark and 2:18sec mark.
Check it out:
[youtube]http://www.youtube.com/watch?v=7kEw0lRtk68[/youtube]