QML compare() does not reliably compare colours

See upstream bug https://bugreports.qt.io/browse/QTBUG-34878

There is already a fix upstream which has been merged to Qt5.8 ( see https://codereview.qt-project.org/#/c/158967/ )
Without that fix, all the unit tests relying on compare() to compare colours must be considered unreliable and potentially misleading, as they could be producing PASSes instead of FAILs.

Bug description copied from that link:
"QtTest's compare() function considers two colors (the QML basic type) as equal when they aren't.
I am aware that Qt.colorEqual exists (and it works correctly), but I think that this makes it far too easy to write tests that don't catch an error.
Consider the following test case:

import QtQuick 2.2
import QtTest 1.0

Item {
    Rectangle {
        id: black
        color: "#000000"
    }

    Rectangle {
        id: white
        color: "#ffffff"
    }

    TestCase {
        name: "ColorComparison"

        function test_this_should_fail() {
            compare(black.color, white.color)
        }

        function test_this_is_ok() {
            compare(black.color == white.color, false)
            compare(Qt.colorEqual(black.color, white.color), false)
        }
    }
}"