ΔE 10.8, fair: the same colour family, but not a straight swap. Prussian Blue is more muted than Kantor Blue.
Can I use Prussian Blue instead of Kantor Blue?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Prussian Blue is more muted than Kantor Blue.
Can I use Kantor Blue instead of Prussian Blue?
The same difference applies the other way round: Kantor Blue is 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.