Well, I must have been sitting under a rock because I missed the fact that Ammo of MIG has come out with a range of colors for Early War Japanese AFV's. I have some enamel paints covering Japanese colors, but I generally prefer acrylic for my airbrushing unless I can't help it because of the fumes associated with enamel painting.
The set appears to include the four primary colors you'll need to paint Japanese tanks from 1937-42 - just what you need to finish up that Rising Sun army! Included is the base khaki (tsuchi kusa iro), the mahogany brown (tsuchi iro), green (kusa iro), as well as flat yellow.
I have an early war tournament coming up early next year and I'm still trying to decide between Japanese and Soviet... yes, you read that right, I'm actually not planning on bringing German... for once!