ΔE 10.6, fair: the same colour family, but not a straight swap. Dark Green 2 (IJN) is more muted, cooler than Castellan Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Dark Green 2 (IJN) is more muted, cooler than Castellan Green.
The same difference applies the other way round: Castellan Green 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 Castellan Green on the colour wheel See Dark Green 2 (IJN) on the colour wheel
All matches: Castellan Green equivalents · Dark Green 2 (IJN) equivalents