Red Copper vs Dark Bronze

How close are they?

ΔE 16.5, loose: different enough that you should pick on purpose. Dark Bronze is more muted, warmer than Red Copper.

Can I use Dark Bronze instead of Red Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Dark Bronze is more muted, warmer than Red Copper.

Can I use Red Copper instead of Dark Bronze?

The same difference applies the other way round: Red Copper is 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.