RGB is coming direct from the chips so it'll be the best quality.
Maybe since you've been using composite or RF with their garish bleeding colours ramped up the transission is noticeable.
On my TV you can't increase the 'colour' when in RGB mode as the A1200 is giving you exactly the colour you're supposed to see.
Maybe your Workbench colour palette needs tweaking, although if games appear pastel hued then something's wrong. Most games are fairly garish!
:-)
Also, when you're in RGB there's no question of whether a foreign Amiga will be to blame on a different country's TV since that only applies to PAL/NTSC via the RF and composite out.
Maybe inserting and removing the SCART socket a few times might wear off any tarnish on the contacts.
BTW, you don't have an internal scandoubler do you?