User blog comment:Xilinoc/Ch. 608 - whatever the title of this one is/@comment-24726378-20141204193451/@comment-1268838-20141205010036

I think it's more the idea that the salamander is black.

I'm inclined to think that Mangastream's translation is more correct. Ichimonji draws its power from all that is "black." The salamander, Urahara's hat and coat, the uniforms of the dead Shinigami, and Yhwach's cloak... all of it was black. And not just in the "oh everything in the manga is in black and white" kind of way.