Look in the DVD set-up menu and look for a setting such as 'Video Output' or 'Connections'.
If there is an option to select RBG or Video output,..and it is currently set to RBG,... then just try the Video setting instead.
(Note generally RBG is the better setting, if available.. or working!).
If this cures the problem, then usually it will be because either your scart cable is not sitting well in the socket, (cheap cables are notorious for this, as the pins tend to be very thin and flimsy, but also look for bent pins) or the socket itself (either TV or DVD end) is damaged.
Otherwise, you may have a fault in the RBG process.
Another possible problem is conflict with the TV's Teletext (assuming it has Teletext) as this is also an RGB process.
In this case you can disconnect the RBG output pins in the Scart Lead. (RGB Out from TV). Scart Pins... 7-Blue, 11-Green, and 15-Red.
Cobweb
January 2007