Neptune Glow vs Blue Horror

How close are they?

ΔE 17.2, loose: different enough that you should pick on purpose. Blue Horror is more muted, cooler than Neptune Glow.

Can I use Blue Horror instead of Neptune Glow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Blue Horror is more muted, cooler than Neptune Glow.

Can I use Neptune Glow instead of Blue Horror?

The same difference applies the other way round: Neptune Glow is more saturated, 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.