ΔE 6.9, close: similar, with a visible difference side by side. Titanium White is a little lighter than Wrack White.
Can I use Titanium White instead of Wrack White?
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Titanium White is a little lighter than Wrack White.
Can I use Wrack White instead of Titanium White?
The same difference applies the other way round: Wrack White is a little darker.
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.