ΔE 13.9, fair: the same colour family, but not a straight swap. Mechanicus Standard Grey is a little darker, much more muted than Bluish Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Mechanicus Standard Grey is a little darker, much more muted than Bluish Grey.
The same difference applies the other way round: Bluish Grey is a little lighter, much 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.
See Bluish Grey on the colour wheel See Mechanicus Standard Grey on the colour wheel
All matches: Bluish Grey equivalents · Mechanicus Standard Grey equivalents