Bluebird Grey vs Light Violet

How close are they?

ΔE 21.9, loose: different enough that you should pick on purpose. Light Violet is noticeably lighter, much more saturated than Bluebird Grey.

Can I use Light Violet instead of Bluebird Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Light Violet is noticeably lighter, much more saturated than Bluebird Grey.

Can I use Bluebird Grey instead of Light Violet?

The same difference applies the other way round: Bluebird Grey is noticeably darker, much more muted.

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.