ΔE 12.5, fair: the same colour family, but not a straight swap. Purple Ink is noticeably darker, more muted than Druchii Violet. They are different kinds of paint: Citadel Druchii Violet is a wash/shade and Reaper Purple Ink 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 13). Purple Ink is noticeably darker, more muted than Druchii Violet. They are different kinds of paint.
The same difference applies the other way round: Druchii Violet is noticeably 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 Druchii Violet on the colour wheel See Purple Ink on the colour wheel
All matches: Druchii Violet equivalents · Purple Ink equivalents