ΔE 12.0, fair: the same colour family, but not a straight swap. Amethyst Purple is a little lighter, more muted, cooler than Kakophoni Purple. They are different kinds of paint: Citadel Kakophoni Purple is an opaque base/layer paint and Green Stuff World Amethyst Purple is an ink, glaze or transparent 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 12). Amethyst Purple is a little lighter, more muted, cooler than Kakophoni Purple. They are different kinds of paint.
The same difference applies the other way round: Kakophoni Purple is a little darker, 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.
See Kakophoni Purple on the colour wheel See Amethyst Purple on the colour wheel
All matches: Kakophoni Purple equivalents · Amethyst Purple equivalents