ΔE 27.2, loose: different enough that you should pick on purpose. Iridescent Bright Gold (Fine) is noticeably lighter, more muted than Retributor Armour. They are different kinds of paint: Citadel Retributor Armour is a metallic and Golden Iridescent Bright Gold (Fine) is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Iridescent Bright Gold (Fine) is noticeably lighter, more muted than Retributor Armour. They are different kinds of paint.
The same difference applies the other way round: Retributor Armour is noticeably 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 Retributor Armour on the colour wheel See Iridescent Bright Gold (Fine) on the colour wheel
All matches: Retributor Armour equivalents · Iridescent Bright Gold (Fine) equivalents