ΔE 11.0, fair: the same colour family, but not a straight swap. Runefang Steel is noticeably darker than Fairy Dust.
Can I use Runefang Steel instead of Fairy Dust?
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Runefang Steel is noticeably darker than Fairy Dust.
Can I use Fairy Dust instead of Runefang Steel?
The same difference applies the other way round: Fairy Dust is noticeably lighter.
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.