However, when appearing inside a form alongside native controls, there is a notable look-and-feel mismatch: default font and anti-aliasing, individual controls such as checkboxes and radio buttons, adornments such as scroll bars and their elements.
The Synth look and feel, the newest addition to Swing introduced in Java 5.0. Synth lets developers rapidly create and deploy custom looks for an application by introducing the concept of a "skin" to Java UI programming.
It allows to create a custom look-and-feel declaratively in an XML file, where complex graphics is defined using images.
Here's an example of a (programmatic) Ocean theme and a (declarative) custom Synth theme.
There are many existing Synth themes, which can be emulated.
Advanced Synth - Custom UIs are a breeze with the newest Swing look and feel, IBM developerWorks
The Synth Look and Feel, Java Desktop, by Scott Violet is Sun's original presentation on Synth