True Copper vs Dark Copper

How close are they?

ΔE 28.1, loose: different enough that you should pick on purpose. Dark Copper is a little lighter, much more muted than True Copper.

Can I use Dark Copper instead of True Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Dark Copper is a little lighter, much more muted than True Copper.

Can I use True Copper instead of Dark Copper?

The same difference applies the other way round: True 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.