Necron Compound vs Iridescent Pearl (Fine)

How close are they?

ΔE 29.4, loose: different enough that you should pick on purpose. Iridescent Pearl (Fine) is noticeably lighter than Necron Compound. They are different kinds of paint: Citadel Necron Compound is a metallic and Golden Iridescent Pearl (Fine) is a pearl paint, so they won’t behave the same on the model even where the colour is close.

Can I use Iridescent Pearl (Fine) instead of Necron Compound?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Iridescent Pearl (Fine) is noticeably lighter than Necron Compound. They are different kinds of paint.

Can I use Necron Compound instead of Iridescent Pearl (Fine)?

The same difference applies the other way round: Necron Compound is noticeably 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.