Bluegrey Dusk vs Dark Prussian Blue

How close are they?

ΔE 6.8, close: similar, with a visible difference side by side. Dark Prussian Blue is warmer than Bluegrey Dusk.

Can I use Dark Prussian Blue instead of Bluegrey Dusk?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Dark Prussian Blue is warmer than Bluegrey Dusk.

Can I use Bluegrey Dusk instead of Dark Prussian Blue?

The same difference applies the other way round: Bluegrey Dusk is cooler.

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.