Sky Blue vs Amulet Aqua

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Amulet Aqua is more saturated, warmer than Sky Blue.

Can I use Amulet Aqua instead of Sky Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Amulet Aqua is more saturated, warmer than Sky Blue.

Can I use Sky Blue instead of Amulet Aqua?

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