ΔE 13.4, fair: the same colour family, but not a straight swap. Rusty Metal is a little darker, more muted, warmer than Iridescent Gold (Fine). They are different kinds of paint: Golden Iridescent Gold (Fine) is a pearl paint and Vallejo Rusty Metal 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 13). Rusty Metal is a little darker, more muted, warmer than Iridescent Gold (Fine). They are different kinds of paint.
The same difference applies the other way round: Iridescent Gold (Fine) is a little lighter, more saturated, cooler.
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 Gold (Fine) on the colour wheel See Rusty Metal on the colour wheel
All matches: Iridescent Gold (Fine) equivalents · Rusty Metal equivalents