Deep Black vs Hospitallier Black

How close are they?

ΔE 7.3, close: similar, with a visible difference side by side. Hospitallier Black is a little darker than Deep Black.

Can I use Hospitallier Black instead of Deep Black?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Hospitallier Black is a little darker than Deep Black.

Can I use Deep Black instead of Hospitallier Black?

The same difference applies the other way round: Deep Black is a little lighter.

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.