Blue Tone vs Vicious Purple

How close are they?

ΔE 31.6, loose: different enough that you should pick on purpose. Vicious Purple is noticeably lighter, more saturated, warmer than Blue Tone.

Can I use Vicious Purple instead of Blue Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 32). Vicious Purple is noticeably lighter, more saturated, warmer than Blue Tone.

Can I use Blue Tone instead of Vicious Purple?

The same difference applies the other way round: Blue Tone is noticeably darker, more muted, 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.