Graugrün RLM 74 vs Mechanicus Standard Grey

How close are they?

ΔE 9.6, close: similar, with a visible difference side by side. Mechanicus Standard Grey is a little darker than Graugrün RLM 74.

Can I use Mechanicus Standard Grey instead of Graugrün RLM 74?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Mechanicus Standard Grey is a little darker than Graugrün RLM 74.

Can I use Graugrün RLM 74 instead of Mechanicus Standard Grey?

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