ΔE 17.5, loose: different enough that you should pick on purpose. IDF/IAF Green is a little lighter, more saturated than Granite Grey.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). IDF/IAF Green is a little lighter, more saturated than Granite Grey.
The same difference applies the other way round: Granite Grey is a little darker, more muted.
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 Granite Grey on the colour wheel See IDF/IAF Green on the colour wheel
All matches: Granite Grey equivalents · IDF/IAF Green equivalents