Autumn Sage vs Grey Green

How close are they?

ΔE 20.3, loose: different enough that you should pick on purpose. Grey Green is noticeably darker, much more muted, warmer than Autumn Sage.

Can I use Grey Green instead of Autumn Sage?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Grey Green is noticeably darker, much more muted, warmer than Autumn Sage.

Can I use Autumn Sage instead of Grey Green?

The same difference applies the other way round: Autumn Sage is noticeably lighter, much 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.