You install new KDE-4.5 and conky’s background seems to be different then you real wallpaper? You lost transparency effect.Everything what you need to know and do is using cmd program feh which should be able to redraw your current wallpaper for conky.
The best idea is write script like this one:
feh --bg-scale "`grep 'wallpaper=' ~/.kde4/share/config/plasma-appletsrc | tail --bytes=+11`"
After execute it conky should automatically update background for right one. Unfortunately you need to run is every time when you change wallpaper.
You need emerge an application: media-gfx/feh. I spotted that it works only for :