Mechanicus Standard Grey vs N3 Neutral Gray

How close are they?

ΔE 6.9, close: similar, with a visible difference side by side. Our swatches for the two are almost the same.

Can I use N3 Neutral Gray instead of Mechanicus Standard Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). The swatches are almost the same.

Can I use Mechanicus Standard Grey instead of N3 Neutral Gray?

The same difference applies the other way round.

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.