ΔE 37.3, loose: different enough that you should pick on purpose. Green Rust is noticeably darker, much more saturated than Fluor White.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 37). Green Rust is noticeably darker, much more saturated than Fluor White.
The same difference applies the other way round: Fluor White is noticeably lighter, 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.
See Fluor White on the colour wheel See Green Rust on the colour wheel
All matches: Fluor White equivalents · Green Rust equivalents