ΔE 11.4, fair: the same colour family, but not a straight swap. Khaki is a little lighter, more saturated, cooler than Tan (USAF).
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Khaki is a little lighter, more saturated, cooler than Tan (USAF).
The same difference applies the other way round: Tan (USAF) is a little darker, more muted, 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 Tan (USAF) on the colour wheel See Khaki on the colour wheel
All matches: Tan (USAF) equivalents · Khaki equivalents