My question is, why would you want a black rose? I suppose it would be a novelty. Certainly it would provide a definitive contrast to white flowers. I've heard of those wanting to plant a black and white garden. This may be attributed to the current trend toward black and white weddings. There is also the popularity of "goth"... black clothing, black nail polish, black lipstick and hair. All right, I'm willing to concede (reluctantly...I'm stubborn) that just because it's not my taste doesn't discount its value. So I'm off to answer the question if I can.
There exists an International Black Plant Society, so I decided to check them out. It was founded by Karen Platt in the UK for people who love black plants. She has written a book titled "Black Magic and Purple Passion," which is available on her web site. There seems to be some controversy or sour grapes; you can sort it out if you wish. Since I didn't have time to order the book, I moved on.
David Beaulieau at About.com says "Cultivators have been working hard in trying to produce a black rose. While no jet-black rose yet exists, there are some of such a deep red as to suggest black. E.g., Rosa 'Black Magic' and, pictured above, Rosa 'Ruby Celebration. Alternatively, some florists dry fresh roses and dye them black."  He also suggests that it is difficult to assign a meaning to a rose color which really does not exist, but it can mean death including the death of old habits; i.e. a rebirth. Confused yet? So here is one opinion against the existance of the black rose. (Note: I did not have the proper permissions to use the picture of 'Ruby Celebration' indicated in the quote. At left is 'Black Magic'.)
There is always something of interest in Wikipedia, although you have to take the information as is. I found the quote on the symbolism amusing. "But it really means farewell or the overcoming of a long hard journey. They were often used at funerals.", and it continues, "...a true black rose is impossible to produce." We have here another vote against the reality of the true black rose in nature. We also have some funerals devoid of flowers. Several varieties of deep red roses are mentioned including 'Black Magic', pictured above. The others are pictured below; 'Barkarole', aka 'Taboo', and 'Baccara'. I added 'Black Baccara', which is a more recent introduction and a darker version of 'Baccara'.
Returning to the UK, my next stop is at the Flowers & Plants Association. The definitive word from the Brits, who sound so authoritative to me because of the accent (doesn't translate into e-speak though): "In reality no pure black flowers exist." They do make some suggestions about arranging black flowers, including black tulips, which are actually a deep purple. So you can can stop your search for black tulips as well.
I think by now we can all agree that there are no true black roses. The quest goes on with the rose breeders. If you are interested in seeing how popular the black rose is in today's society, just do a web search. I knew it was a popular theme in romance and mystery novels, probably poetry also. There are lots of songs and even band names with 'black rose' in them. Then it gets interesting... tattoo parlour, World of Warcraft guild, non-profit agency, bridal wear, coven, Irish pub, publishing company.
Let's get back to the roses. Here are some more 'almost black', deep, dark, velvety red roses.
Well, this is the last in my 'Roses of Color' series. I hope you have enjoyed the journey as much as I have. There have been so many gorgeous roses and I want them all. I've loved hearing from all of you about your roses, about you getting the courage to buy your first rose, about you making your rose shopping lists from my articles. I'd like to thank jandp for the photo of 'Black Magic' and the other DG rosarians and/or photographers who contributed the fabulous photographs to this article and to all the articles in the series. Bravo! Thanks to you all for indulging me and letting me go on and on about my favorite subject ... ROSES !!
 Beaulieu, David, About.com, Picture of a "Black" Rose
 Wikipedia, the free encycylopedia; Black rose (symbolism)
 Flowers & Plants Association; Black Roses: Magic and Mysticism
 Here are the links to the other articles in my 'Roses of Color' series