ΔE 44.9, loose: different enough that you should pick on purpose. Pearl Yellow is noticeably lighter, much more saturated, cooler than Retributor Armour. They are different kinds of paint: Citadel Retributor Armour is a metallic and Tamiya Pearl Yellow 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 45). Pearl Yellow is noticeably lighter, much more saturated, cooler than Retributor Armour. They are different kinds of paint.
The same difference applies the other way round: Retributor Armour is noticeably darker, much more muted, warmer.
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 Pearl Yellow on the colour wheel
All matches: Retributor Armour equivalents · Pearl Yellow equivalents