Cobalt Metal vs Blue Steel

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Blue Steel is noticeably lighter, warmer than Cobalt Metal.

Can I use Blue Steel instead of Cobalt Metal?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Blue Steel is noticeably lighter, warmer than Cobalt Metal.

Can I use Cobalt Metal instead of Blue Steel?

The same difference applies the other way round: Cobalt Metal is noticeably darker, cooler.

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.