This photo has been taken in early autumn (at the end period of their blooming) and therefor the color of it is a lot lighter than the 'official' one. At it's fool bloom it's quite darker. If the one you have differs only in the darkness of color from this one, then you most probably have the 'Arabian Night'. To my knowledge there's only one dahlia that goes by that name, but in my experience name overlapping is not uncommon so I can not tell for sure.
