ΔE 11.5, fair: the same colour family, but not a straight swap. Demon Blood is a little lighter, more muted than Xereus Purple. They are different kinds of paint: Citadel Xereus Purple is an opaque base/layer paint and Vallejo Demon Blood is a fluorescent or effect paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Demon Blood is a little lighter, more muted than Xereus Purple. They are different kinds of paint.
The same difference applies the other way round: Xereus Purple is a little darker, more saturated.
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.
See Xereus Purple on the colour wheel See Demon Blood on the colour wheel
All matches: Xereus Purple equivalents · Demon Blood equivalents