Prussian Blue vs Regal Blue

How close are they?

ΔE 8.0, close: similar, with a visible difference side by side. Regal Blue is more saturated, cooler than Prussian Blue.

Can I use Regal Blue instead of Prussian Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Regal Blue is more saturated, cooler than Prussian Blue.

Can I use Prussian Blue instead of Regal Blue?

The same difference applies the other way round: Prussian Blue is more muted, warmer.

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.