ΔE 13.7, fair: the same colour family, but not a straight swap. Mechanicus Standard Grey is a little lighter than IJN D1 Deep Green Black.
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 lighter than IJN D1 Deep Green Black.
The same difference applies the other way round: IJN D1 Deep Green Black 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 IJN D1 Deep Green Black on the colour wheel See Mechanicus Standard Grey on the colour wheel
All matches: IJN D1 Deep Green Black equivalents · Mechanicus Standard Grey equivalents