ΔE 5.9, very close: most people won’t see a difference side by side. Stormhost Silver is a little lighter than Runefang Steel.
Can I use Stormhost Silver instead of Runefang Steel?
Yes, for most jobs. Very close match (ΔE 6). Stormhost Silver is a little lighter than Runefang Steel.
Can I use Runefang Steel instead of Stormhost Silver?
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.