To reproduce this, run the following on a Windows 10 system with HiDPI scaling of 125%. It will fail some of the time (about 1/3 of the time on my system).

$ gradle --info -PFULL_TEST=true -PUSE_ROBOT=true cleanTest :systemTests:test --tests RobotTest.testPixelCaptureAverage

test.robot.javafx.scene.RobotTest > testPixelCaptureAverage FAILED
    junit.framework.AssertionFailedError: expected: rgba(0,0,255,255) but was: rgba(255,0,0,255)
        at test.robot.javafx.scene.RobotTest.assertColorEquals(RobotTest.java:839)
        at test.robot.javafx.scene.RobotTest.testPixelCaptureAverage(RobotTest.java:695)