ΔE 11.1, fair: the same colour family, but not a straight swap. Russian AF Grey N.4 is more muted, cooler than Thar Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Russian AF Grey N.4 is more muted, cooler than Thar Brown.
The same difference applies the other way round: Thar Brown is more saturated, 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 Thar Brown on the colour wheel See Russian AF Grey N.4 on the colour wheel
All matches: Thar Brown equivalents · Russian AF Grey N.4 equivalents