ΔE 8.6, close: similar, with a visible difference side by side. IDF/IAF Green is more muted than Hemp BS4800/10B21.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). IDF/IAF Green is more muted than Hemp BS4800/10B21.
The same difference applies the other way round: Hemp BS4800/10B21 is more saturated.
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 Hemp BS4800/10B21 on the colour wheel See IDF/IAF Green on the colour wheel
All matches: Hemp BS4800/10B21 equivalents · IDF/IAF Green equivalents