PR, PB and Y is component that can pass progressive. CR, CB and Y is different (interlaced only?), but I don't remember what it's limitation was. There was a discussion here about it not too long ago, maybe a search will turn up that info. According to that article, it looks like scart cannot pass progressive, only s-video and composite. RGB I believe only refers to the cable colors for component video, which are Red, Green and Blue, though I know that the term seems to be more often applied to a cable that has a d-sub on one end (VGA) for use with a PC.