Dark Eternal Night vs The Fang

How close are they?

ΔE 18.9, loose: different enough that you should pick on purpose. The Fang is a little lighter, much more saturated than Dark Eternal Night.

Can I use The Fang instead of Dark Eternal Night?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). The Fang is a little lighter, much more saturated than Dark Eternal Night.

Can I use Dark Eternal Night instead of The Fang?

The same difference applies the other way round: Dark Eternal Night is a little darker, much more muted.

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.