ΔE 11.9, fair: the same colour family, but not a straight swap. Dark Elf Highlight is a little darker, more muted than Slaanesh Grey.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Dark Elf Highlight is a little darker, more muted than Slaanesh Grey.
The same difference applies the other way round: Slaanesh Grey is a little lighter, 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 Slaanesh Grey on the colour wheel See Dark Elf Highlight on the colour wheel
All matches: Slaanesh Grey equivalents · Dark Elf Highlight equivalents