JFrame in spark

Now i meet a problem and request for help!

In the source code of spark, a JFrame has a blue decorate! I meant the JFrame-header color is blue!

And i want to change the color of the JFrame’s header into

Some people said the JFrame’s decorate is rely on the operating system, it means, a JFrame’s header is blue in XP, and vifrification in win7?

And i found an interesting thing: In my win7 operating system, i new a JFrame and it’s header is vifrification. When i new a JFrame in the LoginDialog.java which is one of the source codes, it just comes a blue header, like the guys did in XP operating system!

So, I guess, we can change the JFrame’s header and make it vifrification!

Anyone can help?