ΔE 12.4, fair: the same colour family, but not a straight swap. Plague Brown is noticeably darker, more saturated than Inner Light.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Plague Brown is noticeably darker, more saturated than Inner Light.
The same difference applies the other way round: Inner Light is noticeably lighter, more muted.
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 Inner Light on the colour wheel See Plague Brown on the colour wheel
All matches: Inner Light equivalents · Plague Brown equivalents