JVC LCD pillar-box Problem

I've just got back from helping someone set up their new TV, (a JVC LT-26C31
LCD). Once I'd told the digibox and DVD player to output RGB in widescreen
things looked a lot better, (remind me, just what do the guys from Currys do
in 'setting up' a TV system?...). However I'm left with one problem. When a
4x3 image is pillar-boxed, the TV inserts very annoying bright grey bands,
(curtains), instead of the usual black. I couldn't find anything in the
standard menus to change them to black. Does anyone know how to change these
to be black?

Cheers. Andy C