IJA #3 Hairanshoku (Grey Indigo) vs Green

How close are they?

ΔE 6.4, close: similar, with a visible difference side by side. Green is a little lighter than IJA #3 Hairanshoku (Grey Indigo).

Can I use Green instead of IJA #3 Hairanshoku (Grey Indigo)?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Green is a little lighter than IJA #3 Hairanshoku (Grey Indigo).

Can I use IJA #3 Hairanshoku (Grey Indigo) instead of Green?

The same difference applies the other way round: IJA #3 Hairanshoku (Grey Indigo) is a little darker.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.