ΔE 12.7, fair: the same colour family, but not a straight swap. IJA Light Grey Green is a little darker, more saturated than Longbeard Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). IJA Light Grey Green is a little darker, more saturated than Longbeard Grey.
The same difference applies the other way round: Longbeard Grey is a little 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 Longbeard Grey on the colour wheel See IJA Light Grey Green on the colour wheel
All matches: Longbeard Grey equivalents · IJA Light Grey Green equivalents