Phalanx Blue vs Ashen Blue

How close are they?

ΔE 18.4, loose: different enough that you should pick on purpose. Ashen Blue is a little darker, much more muted than Phalanx Blue.

Can I use Ashen Blue instead of Phalanx Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Ashen Blue is a little darker, much more muted than Phalanx Blue.

Can I use Phalanx Blue instead of Ashen Blue?

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

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.