Deep Blue vs Dark Mica Blue

How close are they?

ΔE 16.4, loose: different enough that you should pick on purpose. Dark Mica Blue is a little darker, much more muted, cooler than Deep Blue.

Can I use Dark Mica Blue instead of Deep Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Dark Mica Blue is a little darker, much more muted, cooler than Deep Blue.

Can I use Deep Blue instead of Dark Mica Blue?

The same difference applies the other way round: Deep Blue is a little lighter, much 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.