Ruinous Spell vs Dark Evergreen

How close are they?

ΔE 15.3, loose: different enough that you should pick on purpose. Dark Evergreen is a little darker, more saturated, warmer than Ruinous Spell.

Can I use Dark Evergreen instead of Ruinous Spell?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Dark Evergreen is a little darker, more saturated, warmer than Ruinous Spell.

Can I use Ruinous Spell instead of Dark Evergreen?

The same difference applies the other way round: Ruinous Spell is a little lighter, more muted, cooler.

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.