JDK-8218479, fix was made to correct the rendering of JTextPane as the background color of JTextPane was similar to Panel color. It looked like the JTextPane has transparent background. No automated test was written to verify the results. Current bug is to write the automated tests for the same.
JDK-8221781 was created to add automated tests for a number of fixes done related to gtk3. The current fix covers JTextPane widget from the widgets listed in JDK-8221781