ΔE 13.7, fair: the same colour family, but not a straight swap. Deep Scarlet Ink is a little darker, cooler than Dark Red Tone. They are different kinds of paint: Army Painter Dark Red Tone is a wash/shade and Nocturna Models Deep Scarlet 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 14). Deep Scarlet Ink is a little darker, cooler than Dark Red Tone. They are different kinds of paint.
The same difference applies the other way round: Dark Red Tone 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 Dark Red Tone on the colour wheel See Deep Scarlet Ink on the colour wheel
All matches: Dark Red Tone equivalents · Deep Scarlet Ink equivalents