ΔE 13.4, fair: the same colour family, but not a straight swap. Mournfang Brown is noticeably darker, warmer than Ruddy Terra.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Mournfang Brown is noticeably darker, warmer than Ruddy Terra.
The same difference applies the other way round: Ruddy Terra is noticeably lighter, 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 Ruddy Terra on the colour wheel See Mournfang Brown on the colour wheel
All matches: Ruddy Terra equivalents · Mournfang Brown equivalents