Hej,
by black theme do mean global colour scheme or kopete theme?
If you mean global colour scheme those can be configured from the control centre -> Appearance & Themes and the configuration files can be found at $HOME/.kde/share/apps/kdisplay/color-schemes/<name-of-the-colour-scheme>.
Configuration files for the kopete styles can be found at $HOME/.kde/share/apps/kopete/styles/<name-of-the-style>.
You might want to take look of those and swing it from there.
Lycka till!
-138-