Neptune Glow vs Hiril Blue

How close are they?

ΔE 15.1, loose: different enough that you should pick on purpose. Hiril Blue is noticeably darker, more saturated, cooler than Neptune Glow.

Can I use Hiril Blue instead of Neptune Glow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Hiril Blue is noticeably darker, more saturated, cooler than Neptune Glow.

Can I use Neptune Glow instead of Hiril Blue?

The same difference applies the other way round: Neptune Glow is noticeably lighter, more muted, 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.