ΔE 12.7, fair: the same colour family, but not a straight swap. Adamantium Black is noticeably darker than Runefang Steel.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Adamantium Black is noticeably darker than Runefang Steel.
The same difference applies the other way round: Runefang Steel is noticeably lighter.
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 Runefang Steel on the colour wheel See Adamantium Black on the colour wheel
All matches: Runefang Steel equivalents · Adamantium Black equivalents