Graugrün RLM 74 vs Dark Reaper

How close are they?

ΔE 8.7, close: similar, with a visible difference side by side. Dark Reaper is more saturated than Graugrün RLM 74.

Can I use Dark Reaper instead of Graugrün RLM 74?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Dark Reaper is more saturated than Graugrün RLM 74.

Can I use Graugrün RLM 74 instead of Dark Reaper?

The same difference applies the other way round: Graugrün RLM 74 is 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.