Stormfiend vs Dusty Blue

How close are they?

ΔE 17.4, loose: different enough that you should pick on purpose. Dusty Blue is noticeably darker, more muted, cooler than Stormfiend.

Can I use Dusty Blue instead of Stormfiend?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Dusty Blue is noticeably darker, more muted, cooler than Stormfiend.

Can I use Stormfiend instead of Dusty Blue?

The same difference applies the other way round: Stormfiend is noticeably lighter, more saturated, warmer.

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.