Stormhost Silver vs Sharkfin Blue

How close are they?

ΔE 15.8, loose: different enough that you should pick on purpose. Sharkfin Blue is noticeably lighter, more saturated than Stormhost Silver.

Can I use Sharkfin Blue instead of Stormhost Silver?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Sharkfin Blue is noticeably lighter, more saturated than Stormhost Silver.

Can I use Stormhost Silver instead of Sharkfin Blue?

The same difference applies the other way round: Stormhost Silver 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.