A lot of people have asked for a "dark color theme" for NetBeans, possibly because there are several attractive dark color schemes for TextMate, a favorite editor among many Ruby developers. Jerrett Taylor has designed and contributed a great dark color theme for NetBeans, "Dark Pastels". I've wrapped it up as a plugin. As of today, it's prebundled with the continuous builds on http://deadlock.netbeans.org/hudson/job/ruby/, but for other versions such as beta1 and the upcoming beta2, you can download the plugin from here and install via Tools | Plugins (go to the Downloaded tab). It should hopefully also appear on the Auto Update center pretty soon.
To switch to this color theme after installing the plugin, open the options dialog, go to "Fonts and Colors" and choose the "Dark Pastels" color theme.
Let's get on to the screenshots! Here's a Ruby file:
...and here's an RHTML file:
Note that the plugin only replaces the editor colors. Other windows such as the navigator and project views keep the general look and feel of the whole application, so you can either slide these off to the side, or install a custom look and feel with colors more to your liking.
Here's what the plugin looks like in the Plugin Manager. As you can see I've named it "Extra Themes" such that it can hold several optional themes, so if you've got a color scheme to share, please do!
A huge thanks to Jerrett!
P.S. The theme the font to "Monaco", which is available on the Mac. If you're on a different platform you may want to go a tweak the default font to one that looks good on your system.