All the pictorial evidence that we have from the Japanese side are a few bits of very poor newsreel-style footage---mostly of Japanese planes taking off from their carriers before the attack. These appear to show that the Zeros and Vals were universally painted in a light gray color----it now appears that this was more like an olive gray, not the very light blue tinted gray one sees in many artists' renditions and kit-makes. The Kates, on the other hand, are often seen with a dark green mottle or blotching, or an overall green top coat, which makes sense considering their primary function as low level attackers. On some Kates---those from the carrier Soryu, in particular---the light blotches have been interpreted as being brown and Japanese experts are adamant about this. As more and more research is done on Pearl Harbor aircraft schemes, it is increasingly clear that the Vals and Kates that took part in the battle, were new machines that were camouflaged about 5-6 weeks beforehand when still at Japanese airbases---not on the carriers while they approached Pearl. Moreover, the Soryu kates seem to have been painted a light tan color, something like mustard in tone, after which a thin green overspray was applied. The latter flaked off very easily when the planes were flown, leaving irregular and splintery light appearing patches--- obviously, revealing the underlying mustard color----that have been interpreted as brown blotches over a green base.
A recent Hobby Master Kate that has reached many collectors, depicts a Soryu Kate in the long assumed brown over green upper surface scheme, with light gray/green on the bottom. I took my Soryu Kate and redid the bottom in a yellow ochre that is a fair representation of "mustard". Then I applied Ochre flakes of various shapes on the upper surface, made the adjacent green look a bit weather worn and added some chipping/weathering effects. The results are shown below: First, here's how Hobby Master's Kate looked as I took it out of its box:
