Purple Tone vs Drakenhof Nightshade

How close are they?

ΔE 18.3, loose: different enough that you should pick on purpose. Drakenhof Nightshade is more muted, cooler than Purple Tone.

Can I use Drakenhof Nightshade instead of Purple Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Drakenhof Nightshade is more muted, cooler than Purple Tone.

Can I use Purple Tone instead of Drakenhof Nightshade?

The same difference applies the other way round: Purple Tone is more saturated, 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.