ΔE 7.5, close: similar, with a visible difference side by side. Pearl Grey is a little lighter than Runefang Steel. They are different kinds of paint: Citadel Runefang Steel is a metallic and Scale75 Pearl Grey is a pearl paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Pearl Grey is a little lighter than Runefang Steel. They are different kinds of paint.
The same difference applies the other way round: Runefang Steel is a little 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.
See Runefang Steel on the colour wheel See Pearl Grey on the colour wheel
All matches: Runefang Steel equivalents · Pearl Grey equivalents