Before I got my Isco lens I used to zoom and my screen wall is painted dark brown. The top of my screen has a bigger black border that helped hide the light from the black bars and at the bottom of my screen I added a 6" wide panel of black self adhesive velvet with a thin piece of hardboard behind it to keep it flat. This also helped with subtitles as it was still possible to read the white text against the black velvet. I did notice that as I progressed from a Panasonic AE2000 then 3000 to the JVC HD350 that the black bar overspill became less and less visible where it hit the brown painted part of the screen wall, so some of the issue is down to having better contrast.
Of course the best solution I've found is to use a lens, so there is no overspill at all. I will now be able to paint my screen wall a lighter colour without it impacting on picture quality (it's our living room) so long as it looks dark with the lights off. Then I might get 'permission'
to paint the other walls a little darker which will
impact on picture quality.