A brand new plugin by the NetBeans Team's window system guru Stan Aubrecht:
Dark theme for Nimbus Look and Feel. It goes well with "Norway Today" editor color scheme. It does not affect other look and feel implementations so you must force Nimbus l&f, i.e., by using --laf Nimbus command line switch. To revert back to the default Nimbus theme just uninstall this module.
In Stan's words, this is a "poor man's" solution. There are some area that would need more tweaking, e.g., the top bar in the Options window. But it would mean changing code in NetBeans. This new module just adjust a few UIManager constants.
I think this is also interesting for any other application based on the NetBeans Platform, especially since the sources are available in the contrib repository:
In particular, look at the ModuleInstall class:
Patches and tweaks are welcome.
Note: You need a very recent build of NetBeans IDE, i.e., NetBeans IDE 7.3 Beta 2 is not recent enough. It needs to be more recent than that, i.e., download the latest NetBeans IDE 7.3 development build to try out this plugin.