ΔE 6.7, close: similar, with a visible difference side by side. Yellow Olive is a little darker than Dark Green BS381C/641.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Yellow Olive is a little darker than Dark Green BS381C/641.
The same difference applies the other way round: Dark Green BS381C/641 is a little lighter.
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 Dark Green BS381C/641 on the colour wheel See Yellow Olive on the colour wheel
All matches: Dark Green BS381C/641 equivalents · Yellow Olive equivalents