Amethyst vs Imperial Purple

How close are they?

ΔE 9.3, close: similar, with a visible difference side by side. Imperial Purple is a little darker than Amethyst.

Can I use Imperial Purple instead of Amethyst?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Imperial Purple is a little darker than Amethyst.

Can I use Amethyst instead of Imperial Purple?

The same difference applies the other way round: Amethyst is a little lighter.

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.