ΔE 17.3, loose: different enough that you should pick on purpose. Cygnar Blue Base is a little darker, more saturated, cooler than Luxion Purple. They are different kinds of paint: Citadel Luxion Purple is a one-coat contrast-style paint and Formula P3 Cygnar Blue Base is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Cygnar Blue Base is a little darker, more saturated, cooler than Luxion Purple. They are different kinds of paint.
The same difference applies the other way round: Luxion Purple is a little lighter, more muted, 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.
See Luxion Purple on the colour wheel See Cygnar Blue Base on the colour wheel
All matches: Luxion Purple equivalents · Cygnar Blue Base equivalents