Autumn Sage vs Pale Lichen

How close are they?

ΔE 18.2, loose: different enough that you should pick on purpose. Pale Lichen is noticeably darker, more muted, cooler than Autumn Sage.

Can I use Pale Lichen instead of Autumn Sage?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Pale Lichen is noticeably darker, more muted, cooler than Autumn Sage.

Can I use Autumn Sage instead of Pale Lichen?

The same difference applies the other way round: Autumn Sage 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.