Necron Compound vs Interference Blue (Fine)

How close are they?

ΔE 36.1, loose: different enough that you should pick on purpose. Interference Blue (Fine) is noticeably lighter, more saturated than Necron Compound. They are different kinds of paint: Citadel Necron Compound is a metallic and Golden Interference Blue (Fine) is a pearl paint, so they won’t behave the same on the model even where the colour is close.

Can I use Interference Blue (Fine) instead of Necron Compound?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 36). Interference Blue (Fine) is noticeably lighter, more saturated than Necron Compound. They are different kinds of paint.

Can I use Necron Compound instead of Interference Blue (Fine)?

The same difference applies the other way round: Necron Compound is noticeably darker, more muted.

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.