The color of the Windows Control of the JFrameInternalFrame is different from the JFrame. The JFrame's Windows Controls should be filled with the Theme's color, the JInternalFrame's windows Controls are filled with Grey color, irrespective of the Theme you have selected.

To reproduce this

- Launch SwingSet2 on Ubuntu on GTK LAF
- On JInternalFrame demo, make on as active, notice the difference in the Window Controls.

Please refer for more details.