Update: this post is for NetBeans 6.1 up to 6.7 This method doesn't work for later NetBeans versions.
I like to personalize my computer and applications. I played around with different color schemes in NetBeans, but I wasn't too happy about the results. But now I have seen two very nice dark color schemes. The first one is Ruby Dark Pastels. The Dark Pastels theme was designed by Jerrett Taylor. We get the scheme if we install the Extra Color Ruby Themes plugin from Tools | Plugins. Now we can go to Tools | Options | Fonts & Colors and select the new color scheme. The following screenshot show the result for a Java source file:
Another very nice theme (and my favorite for now) is the Aloha color theme. We can download the theme as plugin and manually install it in NetBeans using Tools | Plugins | Downloaded. The next screenshot shows the theme for a Java file: 
