ΔE 14.5, fair: the same colour family, but not a straight swap. Ancient Copper is a little darker, much more saturated than True Copper.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Ancient Copper is a little darker, much more saturated than True Copper.
The same difference applies the other way round: True Copper is a little lighter, much more muted.
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.
See True Copper on the colour wheel See Ancient Copper on the colour wheel
All matches: True Copper equivalents · Ancient Copper equivalents