ΔE 10.4, fair: the same colour family, but not a straight swap. Indigo Sky is a little darker, more muted, cooler than Cultist Purple.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Indigo Sky is a little darker, more muted, cooler than Cultist Purple.
The same difference applies the other way round: Cultist Purple is a little lighter, 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 Cultist Purple on the colour wheel See Indigo Sky on the colour wheel
All matches: Cultist Purple equivalents · Indigo Sky equivalents