Brown Green vs Dark Mustard Khaki

How close are they?

ΔE 6.9, close: similar, with a visible difference side by side. Dark Mustard Khaki is more muted, cooler than Brown Green.

Can I use Dark Mustard Khaki instead of Brown Green?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Dark Mustard Khaki is more muted, cooler than Brown Green.

Can I use Brown Green instead of Dark Mustard Khaki?

The same difference applies the other way round: Brown 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.