FULL PRODUCT VERSION :
Microsoft Windows [Version 6.3.9600]
(c) 2013 Microsoft Corporation. All rights reserved.

C:\Users\Owner>java -version
java version "1.8.0_71"
Java(TM) SE Runtime Environment (build 1.8.0_71-b15)
Java HotSpot(TM) Client VM (build 25.71-b15, mixed mode)

C:\Users\Owner>

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows [Version 6.3.9600]
(c) 2013 Microsoft Corporation. All rights reserved.

C:\Users\Owner>ver

Microsoft Windows [Version 6.3.9600]

C:\Users\Owner>

A DESCRIPTION OF THE PROBLEM :
When a JCheckBox is placed on a JToolBar under the Swing look and feel and a few of the derived look and feels, it is painted with no background. This looks odd on the toolbar as it tries to make it behave like a button which it is not.
http://i.imgur.com/dHZ6Yfx.png

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Create a new application and set the default Swing look and feel
2. Create a JToolbar
3. Add a JCheckBox to the JToolBar
4. Run the program and notice the lack of gradient.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I would expected the toolbar to continue painting its gradient background behind the JCheckBox.
ACTUAL -
The JToolBar does not paint the gradient behind the JCheckBox.

REPRODUCIBILITY :
This bug can be reproduced always.

CUSTOMER SUBMITTED WORKAROUND :
It can be corrected by making the checkbox non-opaque, but this should be the default behavior in the SE.
checkbox.setOpaque(false);

An alternative is to set the border to be painted which also makes it less out of place, but the border is still a different color than that for toolbar buttons in the Swing look and feel unless manually overridden.
checkbox.setBorderPainted(true);

SUPPORT :
YES