Previously I had a chart which was on a panel that had a translucent background (styled with CSS). When I upgraded the JRE to 8u20, the chart area was solid white, and no longer translucent.

I will attached a test project to this which will show the issue. In 8u11, the chart will be translucent and you can see the button on the pane below it. In 8u20, the chart background is solid white.