ΔE 15.5, loose: different enough that you should pick on purpose. Flak Gun Yellow is much more saturated, warmer than Desert Webbing.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Flak Gun Yellow is much more saturated, warmer than Desert Webbing.
The same difference applies the other way round: Desert Webbing is much 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 Desert Webbing on the colour wheel See Flak Gun Yellow on the colour wheel
All matches: Desert Webbing equivalents · Flak Gun Yellow equivalents