ΔE 7.5, close: similar, with a visible difference side by side. Wrack White is a little lighter than Spaceship Exterior.
Can I use Wrack White instead of Spaceship Exterior?
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Wrack White is a little lighter than Spaceship Exterior.
Can I use Spaceship Exterior instead of Wrack White?
The same difference applies the other way round: Spaceship Exterior 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.