it's no secret. I use the colorforums hack at my boards, it's written by LK and Allen. There is no version for 6.4, but I talked to LK and he said he should be able to get a version out for 6.6. It's nice cause it allows for a stylechanger (UBBDEV uses a version of colorforums also)
I don't reccomend Colorforums for anyone who isn't very experienced with code, cause I spent more time changing other hacks to work with Colorforums than I did installing the hack itself. If that hack ever catches on, I might look into writing out ports of the hacks I use for others to use.