ΔE 15.2, loose: different enough that you should pick on purpose. Runefang Steel is noticeably darker than Aluminium.
Can I use Runefang Steel instead of Aluminium?
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Runefang Steel is noticeably darker than Aluminium.
Can I use Aluminium instead of Runefang Steel?
The same difference applies the other way round: Aluminium 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.