ΔE 10.5, fair: the same colour family, but not a straight swap. Dark Mustard Khaki is a little lighter, cooler than British Khaki.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Dark Mustard Khaki is a little lighter, cooler than British Khaki.
The same difference applies the other way round: British Khaki is a little darker, 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.
See British Khaki on the colour wheel See Dark Mustard Khaki on the colour wheel
All matches: British Khaki equivalents · Dark Mustard Khaki equivalents