ΔE 11.8, fair: the same colour family, but not a straight swap. Imperial Gold is a little lighter than Iridescent Copper Light (Coarse). They are different kinds of paint: Golden Iridescent Copper Light (Coarse) is a pearl paint and Vallejo Imperial Gold is a metallic, 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 12). Imperial Gold is a little lighter than Iridescent Copper Light (Coarse). They are different kinds of paint.
The same difference applies the other way round: Iridescent Copper Light (Coarse) is a little darker.
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 Iridescent Copper Light (Coarse) on the colour wheel See Imperial Gold on the colour wheel
All matches: Iridescent Copper Light (Coarse) equivalents · Imperial Gold equivalents