It's gray, it's because it was given in a forum where rep doesn't add to your count or from a member with no rep power.
Thanks Guys .. dang I got lots of good reps but all purple Been trying so hard to get my second block .... grrrrrrrrrrrrrr
Rep Given in GC area has a very little effect, and often shows as gray/blue/purple or whatever.... More info - http://forums.digitalpoint.com/showpost.php?p=1616&postcount=8
Not last night, there was no way I could face that, I'm still recovering from the weekend! Damn bank holidays!