--- About ---
Once again - Difficult to categorize this tweak because it is technically a KDE-tweak but it is meant for Digikam under gtk.
I started doing this for Pantheon/elementaryOS, following elementary's dark color set. The bad news is that there's no easy way (I haven't found one yet anyhow) to change Qt-settings under elementaryOS. I tried with "qt4-config" but it didn't seem to affect digikam much.
The thing is that scrollbars etc which are painted by elementary stay with elementary's color scheme, making it hard to see some elements. So if you want Digikam with a dark theme, like this, I suggest switching graphical component style to Breeze or any other you like. That way you will have a solid dark digikam :-)
If you are using another system GTK-theme on elementary you might not have to switch graphical component style. Just make sure the colors match :-P
--- Installation ---
* Extract ElementaryDarkGTK.colors to ~/.kde/share/apps/color-schemes/
* Start/restart Digikam and pick the theme
* Switch Graphical component style