Fluorescent Magenta vs Fluorescent Red

How close are they?

ΔE 55.5, loose: different enough that you should pick on purpose. Fluorescent Red is a little darker, more muted, warmer than Fluorescent Magenta.

Can I use Fluorescent Red instead of Fluorescent Magenta?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 55). Fluorescent Red is a little darker, more muted, warmer than Fluorescent Magenta.

Can I use Fluorescent Magenta instead of Fluorescent Red?

The same difference applies the other way round: Fluorescent Magenta is a little lighter, more saturated, 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.