Blue Sand vs Amethyst Purple

How close are they?

ΔE 27.3, loose: different enough that you should pick on purpose. Amethyst Purple is a little darker, much more saturated, warmer than Blue Sand.

Can I use Amethyst Purple instead of Blue Sand?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Amethyst Purple is a little darker, much more saturated, warmer than Blue Sand.

Can I use Blue Sand instead of Amethyst Purple?

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