ΔE 10.5, fair: the same colour family, but not a straight swap. Asheth Grey is noticeably lighter than Abaddon Black.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Asheth Grey is noticeably lighter than Abaddon Black.
The same difference applies the other way round: Abaddon Black is noticeably 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 Abaddon Black on the colour wheel See Asheth Grey on the colour wheel
All matches: Abaddon Black equivalents · Asheth Grey equivalents