ΔE 10.6, fair: the same colour family, but not a straight swap. Blackroot Grey is more muted than Midnight Olive.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Blackroot Grey is more muted than Midnight Olive.
The same difference applies the other way round: Midnight Olive is 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 Midnight Olive on the colour wheel See Blackroot Grey on the colour wheel
All matches: Midnight Olive equivalents · Blackroot Grey equivalents