Do you or your neighbours have a DECT phone? I experienced problems on
that (and only on that) transponder on Astra 19.2E caused by a DECT base
station near to the sat cabling. Well, actually caused by a shielding
defect in the sat cabling near to the phone base station. In my case,
the picture looked like a bad sat link - rectangular distortions and
still images. Although in your case, it's unlikely that a defective
cable affects only one colour on an encoded signal... - but it might be
worth a try.
Yes, it was DECT (why didn't I get that idea myself?).