ΔE 13.1, fair: the same colour family, but not a straight swap. Paynes Gray is a little darker, more muted than Incubi Darkness.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Paynes Gray is a little darker, more muted than Incubi Darkness.
The same difference applies the other way round: Incubi Darkness is a little 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 Incubi Darkness on the colour wheel See Paynes Gray on the colour wheel
All matches: Incubi Darkness equivalents · Paynes Gray equivalents