Copper vs Gold Brown

How close are they?

ΔE 16.2, loose: different enough that you should pick on purpose. Gold Brown is a little lighter, cooler than Copper.

Can I use Gold Brown instead of Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Gold Brown is a little lighter, cooler than Copper.

Can I use Copper instead of Gold Brown?

The same difference applies the other way round: Copper is a little darker, 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.