Korean association profile here:
흑영(黑英)
It says: "Amami seedling mutation with yellow-green fukurin. Dark green in the center of the leaf, with wide olive green margins that are a bit on the dark side. When grown in high light the centers can become darker, edging on black, increasing the contrast significantly. Because of its restrained variegation, more so than seeing it in photos, seeing it in hand and deliberately examining the plant, you can feel the subtle elegance. Moreover, the leaves are very wide and thick, showing the konoha-gata (lanceolate) outline, overall having a very thick and sturdy form. In Japan, the variety also goes by the names Sōten 蒼天 and Zuirei 瑞麗. Mud root, mud stem, almost wavy straight tsuke."