Asheth Grey vs Luftwaffe Green

How close are they?

ΔE 16.8, loose: different enough that you should pick on purpose. Luftwaffe Green is a little lighter, much more saturated than Asheth Grey.

Can I use Luftwaffe Green instead of Asheth Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Luftwaffe Green is a little lighter, much more saturated than Asheth Grey.

Can I use Asheth Grey instead of Luftwaffe Green?

The same difference applies the other way round: Asheth Grey is a little darker, much more muted.

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.