Also, RGB via Scart will carry composite video, too, either just as a sync signal or as a full video signal. TVs with one Scart input usually accept both signals and either switch automatically (if detected) or need be set manually to RGB mode. TVs with two Scart inputs will usually support RGB on only one of them, while the other one is usually dedicated to composite only and sometimes S-Video.
I once fell into that trap by myself last time I plugged my RGB modded Duo into the wrong one of my TV's two Scart sockets. "What the heck, this is blurry as monkey dung wiped over a safari car's windshield, why are the colors so dull and what's up with that annoying dot crawl interference?". Turns out I was using composite video.