Below, is a photo I borrowed from Google images of Canna indica Tropicanna black, as my leaves have been eaten a little by caterpillars.
And here is the close up of my Canna indica (Tropicanna black) with the same black cardboard background. Notice how the sun shinning on them has brought out the gold colour. This is not visible to the naked eye and I got quite a shock when I saw the photograph. But still very striking.