Sumi-zome is a pigment-dye created from burning various oils, usually made into an ink-stick. This sort of sumi is used in Japanese calligraphy. Kapital has applied it as a yarn dye and turned it into this:

As you can see the dye is uneven to create a texture, albeit a more spring-like feeling through shades of gray.  

Blue selvedge throughout, for the non-indigo denim.

The new Kapital Denim label.