ΔE 7.3, close: similar, with a visible difference side by side. Turquoise is more saturated, warmer than Dark Reaper. They are different kinds of paint: Citadel Dark Reaper is an opaque base/layer paint and Green Stuff World Turquoise is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Turquoise is more saturated, warmer than Dark Reaper. They are different kinds of paint.
The same difference applies the other way round: Dark Reaper 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 Reaper on the colour wheel See Turquoise on the colour wheel
All matches: Dark Reaper equivalents · Turquoise equivalents