ΔE 13.6, fair: the same colour family, but not a straight swap. Demon Red is noticeably lighter than Blood Angels Red. They are different kinds of paint: Citadel Blood Angels Red is a one-coat contrast-style paint and Nocturna Models Demon Red is an opaque base/layer 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 14). Demon Red is noticeably lighter than Blood Angels Red. They are different kinds of paint.
The same difference applies the other way round: Blood Angels Red is noticeably 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.
See Blood Angels Red on the colour wheel See Demon Red on the colour wheel
All matches: Blood Angels Red equivalents · Demon Red equivalents