ΔE 11.7, fair: the same colour family, but not a straight swap. Russian AF Grey N.4 is more muted than Undead Flesh.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Russian AF Grey N.4 is more muted than Undead Flesh.
The same difference applies the other way round: Undead Flesh 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 Undead Flesh on the colour wheel See Russian AF Grey N.4 on the colour wheel
All matches: Undead Flesh equivalents · Russian AF Grey N.4 equivalents