ΔE 20.4, loose: different enough that you should pick on purpose. Sharkfin Blue is noticeably lighter, more saturated than Runefang Steel.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Sharkfin Blue is noticeably lighter, more saturated than Runefang Steel.
The same difference applies the other way round: Runefang Steel is noticeably darker, more muted.
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 Sharkfin Blue on the colour wheel
All matches: Runefang Steel equivalents · Sharkfin Blue equivalents