Dark Mustard Khaki vs Green Brown

How close are they?

ΔE 6.0, close: similar, with a visible difference side by side. Green Brown is more saturated than Dark Mustard Khaki.

Can I use Green Brown instead of Dark Mustard Khaki?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Green Brown is more saturated than Dark Mustard Khaki.

Can I use Dark Mustard Khaki instead of Green Brown?

The same difference applies the other way round: Dark Mustard Khaki is more muted.

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.