Neptune's Fury vs Calth Blue Clear

How close are they?

ΔE 16.3, loose: different enough that you should pick on purpose. Calth Blue Clear is noticeably darker, more muted than Neptune's Fury.

Can I use Calth Blue Clear instead of Neptune's Fury?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Calth Blue Clear is noticeably darker, more muted than Neptune's Fury.

Can I use Neptune's Fury instead of Calth Blue Clear?

The same difference applies the other way round: Neptune's Fury is noticeably lighter, more saturated.

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.