When we released version 10.1.3 one of the new feature was the highlighter button. But in older versions JDeveloper was missing this feature. But, there was an extension that provided this type of variable highlighting - it was developed by Simeon Zverinski and was put on sourceforge.
Several people who used that extension before got used to its functionality and wanted it updated for 10.1.3. The source was out there for them to do this, but for a long time nobody did anything. And then Gonzalo Aguerrevere took the code and updated it. So now you can use this extension in 10.1.3 as well.
It is in the open source center under help->check for updates.
Unlike the built-in highlighter, the extension doesn't require you to click anything to highlight the variable - it does it dynamically.
It also allows you to easily navigate between the coinsurances of the variable using ctrl+alt+ up/down arrows.
So check it out, you might like it.
And thanks Gonzalo for your contribution to the JDeveloper community.