Coven Purple vs Neptune's Fury

How close are they?

ΔE 31.3, loose: different enough that you should pick on purpose. Neptune's Fury is much more saturated, cooler than Coven Purple.

Can I use Neptune's Fury instead of Coven Purple?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Neptune's Fury is much more saturated, cooler than Coven Purple.

Can I use Coven Purple instead of Neptune's Fury?

The same difference applies the other way round: Coven Purple is much more muted, 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.