ΔE 13.7, fair: the same colour family, but not a straight swap. The Darkness is noticeably lighter, more saturated than Matt Black.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). The Darkness is noticeably lighter, more saturated than Matt Black.
The same difference applies the other way round: Matt Black is noticeably darker, more muted.
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 Matt Black on the colour wheel See The Darkness on the colour wheel
All matches: Matt Black equivalents · The Darkness equivalents