Violet Skies vs Blue Violet

How close are they?

ΔE 28.1, loose: different enough that you should pick on purpose. Blue Violet is noticeably darker, cooler than Violet Skies.

Can I use Blue Violet instead of Violet Skies?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 28). Blue Violet is noticeably darker, cooler than Violet Skies.

Can I use Violet Skies instead of Blue Violet?

The same difference applies the other way round: Violet Skies is noticeably lighter, 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.