Brass vs True Copper

How close are they?

ΔE 26.1, loose: different enough that you should pick on purpose. True Copper is noticeably darker, much more saturated, warmer than Brass.

Can I use True Copper instead of Brass?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). True Copper is noticeably darker, much more saturated, warmer than Brass.

Can I use Brass instead of True Copper?

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