Fairy Dust vs Interference Blue (Fine)

How close are they?

ΔE 22.8, loose: different enough that you should pick on purpose. Interference Blue (Fine) is noticeably lighter, more saturated than Fairy Dust. They are different kinds of paint: Army Painter Fairy Dust 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 Fairy Dust?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Interference Blue (Fine) is noticeably lighter, more saturated than Fairy Dust. They are different kinds of paint.

Can I use Fairy Dust instead of Interference Blue (Fine)?

The same difference applies the other way round: Fairy Dust 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.