Autumn Sage vs Caribbean Blue

How close are they?

ΔE 17.0, loose: different enough that you should pick on purpose. Caribbean Blue is much more saturated, cooler than Autumn Sage.

Can I use Caribbean Blue instead of Autumn Sage?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Caribbean Blue is much more saturated, cooler than Autumn Sage.

Can I use Autumn Sage instead of Caribbean Blue?

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