Zephyr Pink vs Copper

How close are they?

ΔE 40.6, loose: different enough that you should pick on purpose. Copper is a little lighter, much more saturated, warmer than Zephyr Pink.

Can I use Copper instead of Zephyr Pink?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 41). Copper is a little lighter, much more saturated, warmer than Zephyr Pink.

Can I use Zephyr Pink instead of Copper?

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