Xereus Purple vs Sapphire Blue

How close are they?

ΔE 27.3, loose: different enough that you should pick on purpose. Sapphire Blue is more muted, cooler than Xereus Purple.

Can I use Sapphire Blue instead of Xereus Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 27). Sapphire Blue is more muted, cooler than Xereus Purple.

Can I use Xereus Purple instead of Sapphire Blue?

The same difference applies the other way round: Xereus Purple is 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.