Night Sky vs Mechanicus Standard Grey

How close are they?

ΔE 6.6, close: similar, with a visible difference side by side. Mechanicus Standard Grey is a little darker, more muted than Night Sky.

Can I use Mechanicus Standard Grey instead of Night Sky?

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

Can I use Night Sky instead of Mechanicus Standard Grey?

The same difference applies the other way round: Night Sky 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.