ΔE 9.8, close: similar, with a visible difference side by side. Royal Purple is a little lighter, more saturated than Leviathan Purple.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Royal Purple is a little lighter, more saturated than Leviathan Purple.
The same difference applies the other way round: Leviathan Purple is a little darker, 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.
See Leviathan Purple on the colour wheel See Royal Purple on the colour wheel
All matches: Leviathan Purple equivalents · Royal Purple equivalents