ΔE 11.6, fair: the same colour family, but not a straight swap. Grey is a little lighter, more muted than Undead Skin.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Grey is a little lighter, more muted than Undead Skin.
The same difference applies the other way round: Undead Skin is a little darker, 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 Skin on the colour wheel See Grey on the colour wheel
All matches: Undead Skin equivalents · Grey equivalents