Xereus Purple vs Cygnar Blue Base

How close are they?

ΔE 23.0, loose: different enough that you should pick on purpose. Cygnar Blue Base is a little lighter, cooler than Xereus Purple.

Can I use Cygnar Blue Base instead of Xereus Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Cygnar Blue Base is a little lighter, cooler than Xereus Purple.

Can I use Xereus Purple instead of Cygnar Blue Base?

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