ΔE 11.4, fair: the same colour family, but not a straight swap. Grey Brown is a little darker, cooler than Shield Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Grey Brown is a little darker, cooler than Shield Brown.
The same difference applies the other way round: Shield 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 Shield Brown on the colour wheel See Grey Brown on the colour wheel
All matches: Shield Brown equivalents · Grey Brown equivalents