ΔE 7.9, close: similar, with a visible difference side by side. RLM 83 Dark Green is a little lighter, more muted, warmer than Ruinous Spell.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). RLM 83 Dark Green is a little lighter, more muted, warmer than Ruinous Spell.
The same difference applies the other way round: Ruinous Spell is a little darker, more saturated, cooler.
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 Ruinous Spell on the colour wheel See RLM 83 Dark Green on the colour wheel
All matches: Ruinous Spell equivalents · RLM 83 Dark Green equivalents