ΔE 10.9, fair: the same colour family, but not a straight swap. Brown is more saturated than Mournfang Brown. They are different kinds of paint: Citadel Mournfang Brown is an opaque base/layer paint and Green Stuff World Brown is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Brown is more saturated than Mournfang Brown. They are different kinds of paint.
The same difference applies the other way round: Mournfang Brown is more muted.
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 Brown on the colour wheel
All matches: Mournfang Brown equivalents · Brown equivalents