ΔE 7.1, close: similar, with a visible difference side by side. Blue Ink is a little darker, warmer than Shadow Thorn. They are different kinds of paint: Army Painter Shadow Thorn is an opaque base/layer paint and Reaper Blue Ink 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). Blue Ink is a little darker, warmer than Shadow Thorn. They are different kinds of paint.
The same difference applies the other way round: Shadow Thorn is a little lighter, 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 Shadow Thorn on the colour wheel See Blue Ink on the colour wheel
All matches: Shadow Thorn equivalents · Blue Ink equivalents