david weaver
Kigami is listed on the yasuki steel page as Yellow.

It's the same as white with a tiny bit more tolerance for silicon, but not enough to consider it as any different (I don't think there's a person alive who could tell the difference between white and yellow in a plane iron).

Aogami - blue
Shirogami - white

Not sure when yasuki mill (now owned by or a sub-brand of hitachi?) made each, but the tolerance for silicon in blue and white is the same.

Blue is (not surprisingly) listed as water or oil hardening. Same spec as white with appx. 0.4% chromium and 1.75% tungsten added.