Gothic Blue vs Prussian Blue Hue

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. Prussian Blue Hue is noticeably darker, more muted than Gothic Blue.

Can I use Prussian Blue Hue instead of Gothic Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Prussian Blue Hue is noticeably darker, more muted than Gothic Blue.

Can I use Gothic Blue instead of Prussian Blue Hue?

The same difference applies the other way round: Gothic Blue is noticeably lighter, 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.