I have some pansys which are almost black in colour

Look at calla lilies, tulip 'Queen of the Night', hollyhock - Alcea rosea 'Nigra', chocolate cosmos, dahlia 'Burgundy Black', helleborus x hybridus cultivars, some of which are a deep purple-black, or a metallic blue/black.

There is a lovely petunia called Black Velvet - Tacca Chantrieri also called Devils or Black Bat Flower - Nemophila Penny Black and Primula Auricular Black Jack.

There is also a lily called 'black pearl'.