ΔE 14.3, fair: the same colour family, but not a straight swap. Slaanesh Grey is a little lighter, more muted than Bright Violet.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Slaanesh Grey is a little lighter, more muted than Bright Violet.
The same difference applies the other way round: Bright Violet is a little darker, more saturated.
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 Bright Violet on the colour wheel See Slaanesh Grey on the colour wheel
All matches: Bright Violet equivalents · Slaanesh Grey equivalents