ΔE 12.7, fair: the same colour family, but not a straight swap. Russian AF Grey N.3 is a little lighter than Brown Gray.
Can I use Russian AF Grey N.3 instead of Brown Gray?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Russian AF Grey N.3 is a little lighter than Brown Gray.
Can I use Brown Gray instead of Russian AF Grey N.3?
The same difference applies the other way round: Brown 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.