ΔE 13.2, fair: the same colour family, but not a straight swap. Chainmail is noticeably lighter than Runefang Steel.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Chainmail is noticeably lighter than Runefang Steel.
The same difference applies the other way round: Runefang Steel 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 Runefang Steel on the colour wheel See Chainmail on the colour wheel
All matches: Runefang Steel equivalents · Chainmail equivalents