Possibly, you either have a loose RGB connection of the scart lead between Digibox and TV (ie. only red connected), or maybe you have CVBS Video/S-Video (input to output) mis-matched.
Make sure scart lead is secure at both ends and/or try a different TV scart input or check it's input setting corresponds to the video output signal from the digibox within the menus.
Cobweb
December 2005