Exile Blue vs Dark Prussian Blue

How close are they?

ΔE 17.6, loose: different enough that you should pick on purpose. Dark Prussian Blue is a little darker, much more muted, warmer than Exile Blue.

Can I use Dark Prussian Blue instead of Exile Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Dark Prussian Blue is a little darker, much more muted, warmer than Exile Blue.

Can I use Exile Blue instead of Dark Prussian Blue?

The same difference applies the other way round: Exile Blue is a little lighter, much more saturated, 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.