ΔE 45.3, loose: different enough that you should pick on purpose. Fluorescent Violet is noticeably darker, much more saturated, warmer than Fluor Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 45). Fluorescent Violet is noticeably darker, much more saturated, warmer than Fluor Blue.
The same difference applies the other way round: Fluor Blue is noticeably lighter, much 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.
See Fluor Blue on the colour wheel See Fluorescent Violet on the colour wheel
All matches: Fluor Blue equivalents · Fluorescent Violet equivalents