What do the symbols mean on the Akatsuki rings mean? I'm stumped.

Itachi     朱 (Vermilion)
Kisame     南 (South)
Pain 零 (rei, "zero")
Konan     白 (White)
Hidan     三 (Three)
Kakuzu     北 (North)
Sasori     玉 (Sphere)
Deidara 青 (Blue)
Zetsu     亥 ("sign of the boar")
Tobi     玉 ("jewel oder ball"; also the black king in shogi)
Orochimaru 空 (Void)
Thats all of them even Ex member

each ring symbol represents their name. Ex: kisame=Vermillion