Dark Green Blue vs Armor Green

How close are they?

ΔE 15.5, loose: different enough that you should pick on purpose. Armor Green is a little darker, warmer than Dark Green Blue.

Can I use Armor Green instead of Dark Green Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Armor Green is a little darker, warmer than Dark Green Blue.

Can I use Dark Green Blue instead of Armor Green?

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