Light Prussian Blue vs Incubi Darkness

How close are they?

ΔE 8.8, close: similar, with a visible difference side by side. Incubi Darkness is a little lighter than Light Prussian Blue.

Can I use Incubi Darkness instead of Light Prussian Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Incubi Darkness is a little lighter than Light Prussian Blue.

Can I use Light Prussian Blue instead of Incubi Darkness?

The same difference applies the other way round: Light Prussian Blue is a little darker.

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.