ΔE 11.3, fair: the same colour family, but not a straight swap. Ruinous Spell is more muted, cooler than IJN Nakajima Dark Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Ruinous Spell is more muted, cooler than IJN Nakajima Dark Green.
The same difference applies the other way round: IJN Nakajima Dark 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 IJN Nakajima Dark Green on the colour wheel See Ruinous Spell on the colour wheel
All matches: IJN Nakajima Dark Green equivalents · Ruinous Spell equivalents