Cobalt Metal vs Sapphire Blue

How close are they?

ΔE 26.3, loose: different enough that you should pick on purpose. Sapphire Blue is a little darker, much more saturated, warmer than Cobalt Metal.

Can I use Sapphire Blue instead of Cobalt Metal?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Sapphire Blue is a little darker, much more saturated, warmer than Cobalt Metal.

Can I use Cobalt Metal instead of Sapphire Blue?

The same difference applies the other way round: Cobalt Metal is a little lighter, much more muted, 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.