ΔE 14.3, fair: the same colour family, but not a straight swap. Permanent Violet Dark is a little darker, more muted, warmer than Magecast Magenta. They are different kinds of paint: Army Painter Magecast Magenta is an opaque base/layer paint and Golden Permanent Violet Dark 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 14). Permanent Violet Dark is a little darker, more muted, warmer than Magecast Magenta. They are different kinds of paint.
The same difference applies the other way round: Magecast Magenta is a little lighter, more saturated, cooler.
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 Magecast Magenta on the colour wheel See Permanent Violet Dark on the colour wheel
All matches: Magecast Magenta equivalents · Permanent Violet Dark equivalents