ΔE 17.1, loose: different enough that you should pick on purpose. Flat Blue is noticeably darker, more saturated, cooler than Bright Violet.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Flat Blue is noticeably darker, more saturated, cooler than Bright Violet.
The same difference applies the other way round: Bright Violet is noticeably 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.
See Bright Violet on the colour wheel See Flat Blue on the colour wheel
All matches: Bright Violet equivalents · Flat Blue equivalents