Dark Violet vs Dark Purple

How close are they?

ΔE 6.8, close: similar, with a visible difference side by side. Dark Purple is a little lighter, more muted, cooler than Dark Violet.

Can I use Dark Purple instead of Dark Violet?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Dark Purple is a little lighter, more muted, cooler than Dark Violet.

Can I use Dark Violet instead of Dark Purple?

The same difference applies the other way round: Dark Violet is a little darker, more saturated, warmer.

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.