Smalt Hue vs Alien Purple

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. Alien Purple is noticeably darker, more saturated, warmer than Smalt Hue.

Can I use Alien Purple instead of Smalt Hue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Alien Purple is noticeably darker, more saturated, warmer than Smalt Hue.

Can I use Smalt Hue instead of Alien Purple?

The same difference applies the other way round: Smalt Hue is noticeably lighter, 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.