Mechanicus Standard Grey vs Doom Death Black

How close are they?

ΔE 6.8, close: similar, with a visible difference side by side. Doom Death Black is a little darker, more muted than Mechanicus Standard Grey.

Can I use Doom Death Black instead of Mechanicus Standard Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Doom Death Black is a little darker, more muted than Mechanicus Standard Grey.

Can I use Mechanicus Standard Grey instead of Doom Death Black?

The same difference applies the other way round: Mechanicus Standard Grey is a little lighter, more saturated.

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.