Plum vs Hexed Lichen

How close are they?

ΔE 17.3, loose: different enough that you should pick on purpose. Hexed Lichen is noticeably darker, more muted, cooler than Plum.

Can I use Hexed Lichen instead of Plum?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Hexed Lichen is noticeably darker, more muted, cooler than Plum.

Can I use Plum instead of Hexed Lichen?

The same difference applies the other way round: Plum is noticeably lighter, more saturated, 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.