Bright Gold vs Gold Brown

How close are they?

ΔE 27.2, loose: different enough that you should pick on purpose. Gold Brown is noticeably darker, much more muted, warmer than Bright Gold.

Can I use Gold Brown instead of Bright Gold?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Gold Brown is noticeably darker, much more muted, warmer than Bright Gold.

Can I use Bright Gold instead of Gold Brown?

The same difference applies the other way round: Bright Gold 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.