ΔE 8.5, close: similar, with a visible difference side by side. Cam. Black Brown is a little lighter, more muted than Nightshade Purple.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Cam. Black Brown is a little lighter, more muted than Nightshade Purple.
The same difference applies the other way round: Nightshade Purple is a little darker, 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 Nightshade Purple on the colour wheel See Cam. Black Brown on the colour wheel
All matches: Nightshade Purple equivalents · Cam. Black Brown equivalents