ΔE 6.8, close: similar, with a visible difference side by side. Amethyst Rose is a little darker, cooler than Mournfang Brown.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Amethyst Rose is a little darker, cooler than Mournfang Brown.
The same difference applies the other way round: Mournfang Brown is a little lighter, warmer.
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 Mournfang Brown on the colour wheel See Amethyst Rose on the colour wheel
All matches: Mournfang Brown equivalents · Amethyst Rose equivalents