ΔE 9.2, close: similar, with a visible difference side by side. Flat White is a little lighter, more muted than Wrack White.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Flat White is a little lighter, more muted than Wrack White.
The same difference applies the other way round: Wrack White is a little darker, more saturated.
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 Wrack White on the colour wheel See Flat White on the colour wheel
All matches: Wrack White equivalents · Flat White equivalents