ΔE 11.5, fair: the same colour family, but not a straight swap. Slate Grey is a little lighter than Mechanicus Standard Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Slate Grey is a little lighter than Mechanicus Standard Grey.
The same difference applies the other way round: Mechanicus Standard Grey is a little darker.
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.
See Mechanicus Standard Grey on the colour wheel See Slate Grey on the colour wheel
All matches: Mechanicus Standard Grey equivalents · Slate Grey equivalents