Ubuntu Jaunty (9.10) has the nice new dark look for the status icons. But this is only working if you use the "Humanity-Dark" icon theme.
I wanted to have another icon theme, but keep the nice dark status icons. So I had a look at the Humanity-Dark icon folder in /usr/share/icons/ and discovered, that this is only an overlay of the normal Humanity icon theme. So this overlay could be used for my favourite icon theme as well. So I just made a copy of the Humanity-Dark folder (if you want to make a new folder in /usr/share/icons you have to be root of course) and changed the name of the new folder to Colors-Dark (because I want to inherit from the gnome colors theme).
In the Colors-Dark folder you have to modify the index.theme file, to use another theme than the Humanity one. First you should change the name to avoid confusion. For example
Name=Colors-Dark. After that the important part comes: change the inherit value to your prefered icon theme. For example
Inherits=gnome-wiseif you want to use gnome wise. That's already everything you have to do. If there is any icon-cache file you better remove and recreate it. You can use gtk-update-icon-cache to create a new cache. Now you have your nice new icons being used, when you choose the Colors-Dark theme, but the dark ubuntu-icons stay.