Violet Coven vs Elfic Blue

How close are they?

ΔE 20.3, loose: different enough that you should pick on purpose. Elfic Blue is more saturated, cooler than Violet Coven.

Can I use Elfic Blue instead of Violet Coven?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Elfic Blue is more saturated, cooler than Violet Coven.

Can I use Violet Coven instead of Elfic Blue?

The same difference applies the other way round: Violet Coven is 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.