I am a believer that cables can make a difference, but I still don't know how a cable can be bright?
A cable simply passes a signal and the best cable would pass it unaltered in any way. I can't see how a cable could boost frequencies, making a cable bright or boomy etc? I can see how it could cut frequencies.
So in other words if a cable is described as bright, this probably means that it is resolving more of the high end in the signal than than another cable was, so it was the other cable that was dulling (attenuating the highs) and it is the one or more of the components in the system that is bright. In this case, a cable that lowers the highs is probably a better match.
I use PS Audio Transcendent and Reference XLR's as well a Ultimate Cables C4s.