ΔE 10.6, fair: the same colour family, but not a straight swap. Transparent Purple is a little darker, cooler than Diabolic Plum. They are different kinds of paint: Army Painter Diabolic Plum is an opaque base/layer paint and Green Stuff World Transparent Purple 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 11). Transparent Purple is a little darker, cooler than Diabolic Plum. They are different kinds of paint.
The same difference applies the other way round: Diabolic Plum is a little lighter, 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 Diabolic Plum on the colour wheel See Transparent Purple on the colour wheel
All matches: Diabolic Plum equivalents · Transparent Purple equivalents