ΔE 12.1, fair: the same colour family, but not a straight swap. AMT-1 Lt. Grey. Brown is a little lighter than Field Gray.
Can I use AMT-1 Lt. Grey. Brown instead of Field Gray?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). AMT-1 Lt. Grey. Brown is a little lighter than Field Gray.
Can I use Field Gray instead of AMT-1 Lt. Grey. Brown?
The same difference applies the other way round: Field Gray is a little darker.
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.