Regal Blue vs Prussian Blue Hue

How close are they?

ΔE 22.8, loose: different enough that you should pick on purpose. Prussian Blue Hue is noticeably darker, more muted, warmer than Regal Blue.

Can I use Prussian Blue Hue instead of Regal Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Prussian Blue Hue is noticeably darker, more muted, warmer than Regal Blue.

Can I use Regal Blue instead of Prussian Blue Hue?

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