ΔE 31.4, loose: different enough that you should pick on purpose. Runefang Steel is noticeably darker, much more muted than Pearl. They are different kinds of paint: AK Interactive Pearl is a pearl paint and Citadel Runefang Steel is a metallic, 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 31). Runefang Steel is noticeably darker, much more muted than Pearl. They are different kinds of paint.
The same difference applies the other way round: Pearl is noticeably lighter, much 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 Pearl on the colour wheel See Runefang Steel on the colour wheel
All matches: Pearl equivalents · Runefang Steel equivalents