Xereus Purple vs Dark Blue

How close are they?

ΔE 18.0, loose: different enough that you should pick on purpose. Dark Blue is a little darker, cooler than Xereus Purple.

Can I use Dark Blue instead of Xereus Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Dark Blue is a little darker, cooler than Xereus Purple.

Can I use Xereus Purple instead of Dark Blue?

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