Copper vs Gold Brown

How close are they?

ΔE 25.4, loose: different enough that you should pick on purpose. Gold Brown is a little lighter, much more muted than Copper.

Can I use Gold Brown instead of Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Gold Brown is a little lighter, much more muted than Copper.

Can I use Copper instead of Gold Brown?

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

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.