ΔE 8.7, close: similar, with a visible difference side by side. Mustard Brown is a little darker, more saturated, warmer than Deep Khaki Drill.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Mustard Brown is a little darker, more saturated, warmer than Deep Khaki Drill.
The same difference applies the other way round: Deep Khaki Drill is a little lighter, more muted, 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 Deep Khaki Drill on the colour wheel See Mustard Brown on the colour wheel
All matches: Deep Khaki Drill equivalents · Mustard Brown equivalents