ΔE 10.3, fair: the same colour family, but not a straight swap. Wrack White is a little lighter than Light Blue.
Can I use Wrack White instead of Light Blue?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Wrack White is a little lighter than Light Blue.
Can I use Light Blue instead of Wrack White?
The same difference applies the other way round: Light Blue 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.