ΔE 12.8, fair: the same colour family, but not a straight swap. Iridescent Gold Deep (Fine) is a little lighter, more muted than True Copper. They are different kinds of paint: Army Painter True Copper is a metallic and Golden Iridescent Gold Deep (Fine) is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Iridescent Gold Deep (Fine) is a little lighter, more muted than True Copper. They are different kinds of paint.
The same difference applies the other way round: True Copper is a little darker, 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.
See True Copper on the colour wheel See Iridescent Gold Deep (Fine) on the colour wheel
All matches: True Copper equivalents · Iridescent Gold Deep (Fine) equivalents