ΔE 15.4, loose: different enough that you should pick on purpose. Ivory is a little lighter, more muted, warmer than Grotesque Green.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Ivory is a little lighter, more muted, warmer than Grotesque Green.
The same difference applies the other way round: Grotesque Green is a little darker, 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 Grotesque Green on the colour wheel See Ivory on the colour wheel
All matches: Grotesque Green equivalents · Ivory equivalents