I know very little about Hoya sp. Black Leaves EPC-301 other than it has an Epiphytica accession number and hails from Prachinburi Province in Thailand. As you can see above, the leaves are far from black. The only thing I can suppose is that new growth when grown in extremely bright light, may come in a very dark color. I for one have not seen it. I have however seen a strong reddish tint to the leaves and good coloration with dark leaf margins on new foliage.
Although the flowers are similar to many other Hoyas, Hoya sp. Black Leaves EPC-301 has its own charms with beautiful, shiny, speckled, leaves and an outstanding scent. If you don’t own another plant with the same type of flowers, I can recommend picking one of these up. It flowers in two years from cutting and will produce a very nice specimen plant in a short time.