Occasionally (perhaps 10% or 15% of the time), the nightly test run will fail with the following error message:

javafx.embed.swing.RT30650Test > test STANDARD_OUT
    detected color: java.awt.Color[r=0,g=0,b=0]
Gradle Worker 66 finished executing tests.

javafx.embed.swing.RT30650Test > test FAILED
    junit.framework.AssertionFailedError: null
        at junit.framework.Assert.fail(Assert.java:47)
        at junit.framework.Assert.assertTrue(Assert.java:20)
        at junit.framework.Assert.assertTrue(Assert.java:27)
        at javafx.embed.swing.RT30650Test.test(RT30650Test.java:38)

This test uses AWT robot to read back the pixels. When it fails, the actual pixel color is BLACK, but the expected color is RED.