Dark Reaper vs Gray Green (Luftwaffe)

How close are they?

ΔE 6.2, close: similar, with a visible difference side by side. Gray Green (Luftwaffe) is a little lighter than Dark Reaper.

Can I use Gray Green (Luftwaffe) instead of Dark Reaper?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Gray Green (Luftwaffe) is a little lighter than Dark Reaper.

Can I use Dark Reaper instead of Gray Green (Luftwaffe)?

The same difference applies the other way round: Dark Reaper 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.