ΔE 11.9, fair: the same colour family, but not a straight swap. Muddy Brown is more muted than Strong Tone. They are different kinds of paint: Army Painter Strong Tone is a wash/shade and Reaper Muddy 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 12). Muddy Brown is more muted than Strong Tone. They are different kinds of paint.
The same difference applies the other way round: Strong Tone is more saturated.
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 Tone on the colour wheel See Muddy Brown on the colour wheel
All matches: Strong Tone equivalents · Muddy Brown equivalents