there's two types of cables.
composite over sync
clear composite over sync. (csync)
the first one is the normal RGB signal cable that we see everywhere.. it works fine and the image quality is very good. the aspect in this cable is that the yelow cable (composite) caries the sync signal and the green and red and blue too again. the red, and green and blue appears two times.
Despite the fact that the TV ignores the RGB signals form the composite wire and focus on the separeted wires, sometimes there may be interferences.
and thinking on that, some people develop a second RGB cable, and call it, TRUE RGB Cable...
what they dit is, they force the composite signal (the yellow wire) to go to an chip first (LM 1881), they call it "sync blaster" and can be purchased separetly and instaled in the "normal rgb cable", and this chip will clean the signal by removing the red, green and blue signals and leaving only the information for sync vertical and horizontal..
In the end, it will give a perfect as far as can be image... theres the ultimate RGB.. no more improvements can be done..
They alert that for french secam consoles, this will not work... and choose a normal cable...
looking to they page they say clearly:
Super Nintendo PAL - not work properly.. be aware.
hope this explanation help.