Amber Alchemy vs Gold Brown

How close are they?

ΔE 18.5, loose: different enough that you should pick on purpose. Gold Brown is noticeably darker, much more saturated than Amber Alchemy.

Can I use Gold Brown instead of Amber Alchemy?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Gold Brown is noticeably darker, much more saturated than Amber Alchemy.

Can I use Amber Alchemy instead of Gold Brown?

The same difference applies the other way round: Amber Alchemy is noticeably lighter, much more muted.

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.