Doug -
That Aviation of Japan painting guide looks like an exellent reference. I am going to try to get a copy. Until then, I rely on the late Jim Lansdale's "Zero Camouflage Schemes"
Zero Camouflage Schemes by James F. Lansdale
As for actually capturing what Zero designer Horikoshi Jiro called
hairyokushoku ("dimly-shining ash green"), I figure if it's light gray with a greenish tannish tint, it's probably in the ball park.
Don