ΔE 13.5, fair: the same colour family, but not a straight swap. Chestnut Brown is noticeably lighter, cooler than Strong Skin Wash. They are different kinds of paint: Army Painter Strong Skin Wash is a wash/shade and Nocturna Models Chestnut Brown is an opaque base/layer 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 14). Chestnut Brown is noticeably lighter, cooler than Strong Skin Wash. They are different kinds of paint.
The same difference applies the other way round: Strong Skin Wash is noticeably darker, 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 Strong Skin Wash on the colour wheel See Chestnut Brown on the colour wheel
All matches: Strong Skin Wash equivalents · Chestnut Brown equivalents