Fluor Blue vs Frost

How close are they?

ΔE 30.9, loose: different enough that you should pick on purpose. Frost is noticeably lighter, more muted, cooler than Fluor Blue.

Can I use Frost instead of Fluor Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Frost is noticeably lighter, more muted, cooler than Fluor Blue.

Can I use Fluor Blue instead of Frost?

The same difference applies the other way round: Fluor Blue is noticeably darker, more saturated, 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.