Bright Sapphire vs Blue Horror

How close are they?

ΔE 8.8, close: similar, with a visible difference side by side. Blue Horror is more muted, warmer than Bright Sapphire.

Can I use Blue Horror instead of Bright Sapphire?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Blue Horror is more muted, warmer than Bright Sapphire.

Can I use Bright Sapphire instead of Blue Horror?

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