Feywild Glow vs Vampire Fang

How close are they?

ΔE 19.5, loose: different enough that you should pick on purpose. Vampire Fang is noticeably darker, more muted than Feywild Glow.

Can I use Vampire Fang instead of Feywild Glow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Vampire Fang is noticeably darker, more muted than Feywild Glow.

Can I use Feywild Glow instead of Vampire Fang?

The same difference applies the other way round: Feywild Glow 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.