Lapislazuli vs Dark Blue

How close are they?

ΔE 6.4, close: similar, with a visible difference side by side. Dark Blue is a little lighter than Lapislazuli.

Can I use Dark Blue instead of Lapislazuli?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Dark Blue is a little lighter than Lapislazuli.

Can I use Lapislazuli instead of Dark Blue?

The same difference applies the other way round: Lapislazuli is a little darker.

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.