Kantor Blue vs Malefic Purple

How close are they?

ΔE 16.5, loose: different enough that you should pick on purpose. Malefic Purple is a little darker, much more muted, warmer than Kantor Blue.

Can I use Malefic Purple instead of Kantor Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Malefic Purple is a little darker, much more muted, warmer than Kantor Blue.

Can I use Kantor Blue instead of Malefic Purple?

The same difference applies the other way round: Kantor Blue is a little lighter, much more saturated, 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.