Sapphire Blue vs Blue Horror

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Blue Horror is cooler than Sapphire Blue.

Can I use Blue Horror instead of Sapphire Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Blue Horror is cooler than Sapphire Blue.

Can I use Sapphire Blue instead of Blue Horror?

The same difference applies the other way round: Sapphire Blue is 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.