Pastel Violet vs Blueberry

How close are they?

ΔE 15.5, loose: different enough that you should pick on purpose. Blueberry is a little darker, more saturated, cooler than Pastel Violet.

Can I use Blueberry instead of Pastel Violet?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Blueberry is a little darker, more saturated, cooler than Pastel Violet.

Can I use Pastel Violet instead of Blueberry?

The same difference applies the other way round: Pastel Violet is a little lighter, 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.