ΔE 17.0, loose: different enough that you should pick on purpose. Gengis Khaki is a little darker, more muted, warmer than Greatcoat Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Gengis Khaki is a little darker, more muted, warmer than Greatcoat Green.
The same difference applies the other way round: Greatcoat Green is a little lighter, more saturated, 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 Greatcoat Green on the colour wheel See Gengis Khaki on the colour wheel
All matches: Greatcoat Green equivalents · Gengis Khaki equivalents