I get the following test failure consistently on a relatively new MacBook Pro system (early 2020 model), running macOS 10.15.7.

SwingNodeJDialogTest

test.robot.javafx.embed.swing.SwingNodeJDialogTest > testJDialogAbove FAILED
    java.lang.AssertionError: JDialog is not above JavaFX stage expected:<java.awt.Color[r=0,g=0,b=255]> but was:<java.awt.Color[r=20,g=0,b=255]>
        at org.junit.Assert.fail(Assert.java:91)
        at org.junit.Assert.failNotEquals(Assert.java:645)
        at org.junit.Assert.assertEquals(Assert.java:126)
        at test.robot.javafx.embed.swing.SwingNodeBase.testAbove(SwingNodeBase.java:218)
        at test.robot.javafx.embed.swing.SwingNodeJDialogTest.testJDialogAbove(SwingNodeJDialogTest.java:42)

test.robot.javafx.embed.swing.SwingNodeJDialogTest > testNodeRemovalAfterShow FAILED
    java.lang.AssertionError: JDialog is not above JavaFX stage expected:<java.awt.Color[r=0,g=0,b=255]> but was:<java.awt.Color[r=20,g=0,b=255]>
        at org.junit.Assert.fail(Assert.java:91)
        at org.junit.Assert.failNotEquals(Assert.java:645)
        at org.junit.Assert.assertEquals(Assert.java:126)
        at test.robot.javafx.embed.swing.SwingNodeBase.testAbove(SwingNodeBase.java:218)
        at test.robot.javafx.embed.swing.SwingNodeJDialogTest.testNodeRemovalAfterShow(SwingNodeJDialogTest.java:52)

test.robot.javafx.embed.swing.SwingNodeJDialogTest > testStageCloseAfterShow FAILED
    java.lang.AssertionError: JDialog is not above JavaFX stage expected:<java.awt.Color[r=0,g=0,b=255]> but was:<java.awt.Color[r=20,g=0,b=255]>
        at org.junit.Assert.fail(Assert.java:91)
        at org.junit.Assert.failNotEquals(Assert.java:645)
        at org.junit.Assert.assertEquals(Assert.java:126)
        at test.robot.javafx.embed.swing.SwingNodeBase.testAbove(SwingNodeBase.java:218)
        at test.robot.javafx.embed.swing.SwingNodeJDialogTest.testStageCloseAfterShow(SwingNodeJDialogTest.java:77)

test.robot.javafx.embed.swing.SwingNodeJDialogTest > testStageCloseBeforeShow FAILED
    java.lang.AssertionError: JDialog is not above JavaFX stage expected:<java.awt.Color[r=0,g=0,b=255]> but was:<java.awt.Color[r=20,g=0,b=255]>
        at org.junit.Assert.fail(Assert.java:91)
        at org.junit.Assert.failNotEquals(Assert.java:645)
        at org.junit.Assert.assertEquals(Assert.java:126)
        at test.robot.javafx.embed.swing.SwingNodeBase.testAbove(SwingNodeBase.java:218)
        at test.robot.javafx.embed.swing.SwingNodeJDialogTest.testStageCloseBeforeShow(SwingNodeJDialogTest.java:87)

I suspect some sort of difference in the color profile on that system (in which case this might be closed as not a bug), but will need to check. If not, then we will need to add tolerance to the color check of that test. I note that this particular test uses AWT Robot rather than FX Robot.