Dark Blue vs Hexed Lichen

How close are they?

ΔE 17.8, loose: different enough that you should pick on purpose. Hexed Lichen is a little lighter, more muted, warmer than Dark Blue.

Can I use Hexed Lichen instead of Dark Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Hexed Lichen is a little lighter, more muted, warmer than Dark Blue.

Can I use Dark Blue instead of Hexed Lichen?

The same difference applies the other way round: Dark Blue is a little darker, more saturated, 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.