ΔE 11.1, fair: the same colour family, but not a straight swap. Stormfiend is a little darker, more saturated, warmer than Runic Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Stormfiend is a little darker, more saturated, warmer than Runic Grey.
The same difference applies the other way round: Runic Grey is a little lighter, more muted, cooler.
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 Runic Grey on the colour wheel See Stormfiend on the colour wheel
All matches: Runic Grey equivalents · Stormfiend equivalents