Issue: Pressing the contrast button on the left or middle MFD inverts ONLY the display elements, but not the background. This means the display becomes unusable, as both the background and elements are the same colour. The right MFD works correctly. Recreating: Press the contrast button on the left or central MFD in the class 422 in either RRO or HRR. Photos attached. One photo shows the display in its normal mode (white elements, blue background), whilst the second shows the display after the contrast button had been pressed (the background should be white, but remains blue).