ΔE 13.8, fair: the same colour family, but not a straight swap. Eldandil Violet is more saturated, warmer than Dark Sky.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Eldandil Violet is more saturated, warmer than Dark Sky.
The same difference applies the other way round: Dark Sky is more muted, 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 Dark Sky on the colour wheel See Eldandil Violet on the colour wheel
All matches: Dark Sky equivalents · Eldandil Violet equivalents