Purple Swarm vs Leviathan Purple

How close are they?

ΔE 9.8, close: similar, with a visible difference side by side. Leviathan Purple is a little darker, more muted than Purple Swarm.

Can I use Leviathan Purple instead of Purple Swarm?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Leviathan Purple is a little darker, more muted than Purple Swarm.

Can I use Purple Swarm instead of Leviathan Purple?

The same difference applies the other way round: Purple Swarm is a little lighter, more saturated.

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.