Dark Ivory vs Insignia White

How close are they?

ΔE 7.9, close: similar, with a visible difference side by side. Insignia White is a little lighter, more saturated than Dark Ivory.

Can I use Insignia White instead of Dark Ivory?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Insignia White is a little lighter, more saturated than Dark Ivory.

Can I use Dark Ivory instead of Insignia White?

The same difference applies the other way round: Dark Ivory 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.