During the Victorian and Edwardian times when all things sombre were in fashion the pursuit of black flowers was at an all time high. Today, plants with "black" foliage and flowers are still highly sought after by gardeners and something plant breeders are trying to get to market. In reality, the advances in Photoshop have done more to continue the idea of "black plants" than have advances in plant breeding. A lot of the photos you see in catalogs have been doctored to make the flowers darker than they really are--the flowers & plants may be more of a deep purple or blood red color than black.
Black Plants for Drama in the Garden
A couple of years ago when my grandfather passed away I planted a black garden to help my grandmother with the mourning process. My quest for black flowers and plants, while nothing like that of the Victorians, was rather disappointing. With the exception of the black hollyhocks (which I traded seeds for) these plants pictured below I found in various garden centers in Chicago. They're a mix of annuals & perennials and tropicals.