ΔE 7.6, close: similar, with a visible difference side by side. Ivory is a little lighter, cooler than Ancient Stone.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Ivory is a little lighter, cooler than Ancient Stone.
The same difference applies the other way round: Ancient Stone is a little darker, 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 Ancient Stone on the colour wheel See Ivory on the colour wheel
All matches: Ancient Stone equivalents · Ivory equivalents