Diabolic Plum vs Xereus Purple

How close are they?

ΔE 8.2, close: similar, with a visible difference side by side. Xereus Purple is more saturated than Diabolic Plum.

Can I use Xereus Purple instead of Diabolic Plum?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Xereus Purple is more saturated than Diabolic Plum.

Can I use Diabolic Plum instead of Xereus Purple?

The same difference applies the other way round: Diabolic Plum is more muted.

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.