Alpha Blue vs Amarth Blue

How close are they?

ΔE 16.0, loose: different enough that you should pick on purpose. Amarth Blue is more saturated, cooler than Alpha Blue.

Can I use Amarth Blue instead of Alpha Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Amarth Blue is more saturated, cooler than Alpha Blue.

Can I use Alpha Blue instead of Amarth Blue?

The same difference applies the other way round: Alpha Blue is more muted, 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.