ΔE 12.2, fair: the same colour family, but not a straight swap. Blackstone Void is noticeably darker, more muted than The Darkness.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Blackstone Void is noticeably darker, more muted than The Darkness.
The same difference applies the other way round: The Darkness is noticeably 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.
See The Darkness on the colour wheel See Blackstone Void on the colour wheel
All matches: The Darkness equivalents · Blackstone Void equivalents