On further inspection I think that the Kosjer one is a natural combination too. BUT, there has also been a peice of slate glued to the BBW side of the natural combo.
If you look closely along the edge, you can see a fine/thin amount of coticule yellow mixed halfway into the bottom blue portion. Just next to that there is a line that I think inidcates the glue line. An interesting way of doing things to say the least.