ΔE 8.4, close: similar, with a visible difference side by side. Off-White is a little darker, cooler than Ivory White.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Off-White is a little darker, cooler than Ivory White.
The same difference applies the other way round: Ivory White is a little lighter, 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 Ivory White on the colour wheel See Off-White on the colour wheel
All matches: Ivory White equivalents · Off-White equivalents