Dark Wood vs Copper Brown

How close are they?

ΔE 15.0, loose: different enough that you should pick on purpose. Copper Brown is a little darker, more muted, cooler than Dark Wood.

Can I use Copper Brown instead of Dark Wood?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Copper Brown is a little darker, more muted, cooler than Dark Wood.

Can I use Dark Wood instead of Copper Brown?

The same difference applies the other way round: Dark Wood is a little lighter, more saturated, warmer.

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.