Style of TextField has been changed since jdk7u6

In JDK7fcs-jdk7u5, a plain textfield appears.
In JDK7u6 and later, a dent textfield appears.

Test case is as follows.

--- TextFieldTest.java --->

import java.awt.*;
import java.awt.event.*;

public class TextFieldTest extends Frame {

    TextField tf = new TextField(20);

    public static void main(String ar[]){
        Frame f = new TextFieldTest();
        f.setSize(200,200);
        f.setVisible(true);
    }

    TextFieldTest(){
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

        setLayout(new FlowLayout());
        tf.setBackground(Color.YELLOW);
        add(tf);
    }
}

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Please compile the above test case and run "java TextFieldTest" both in
jdk7u5 and 7u65.
You can see the difference between jdk7u5 and 7u65.