Gray Violet (Luftwaffe) vs IJN Deep Dark Green

How close are they?

ΔE 9.1, close: similar, with a visible difference side by side. IJN Deep Dark Green is a little darker than Gray Violet (Luftwaffe).

Can I use IJN Deep Dark Green instead of Gray Violet (Luftwaffe)?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). IJN Deep Dark Green is a little darker than Gray Violet (Luftwaffe).

Can I use Gray Violet (Luftwaffe) instead of IJN Deep Dark Green?

The same difference applies the other way round: Gray Violet (Luftwaffe) is a little lighter.

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.