Amulet Aqua vs Light Blue

How close are they?

ΔE 18.9, loose: different enough that you should pick on purpose. Light Blue is a little lighter, cooler than Amulet Aqua.

Can I use Light Blue instead of Amulet Aqua?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Light Blue is a little lighter, cooler than Amulet Aqua.

Can I use Amulet Aqua instead of Light Blue?

The same difference applies the other way round: Amulet Aqua is a little darker, 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.