Legendary Red vs Fire Orange

How close are they?

ΔE 22.3, loose: different enough that you should pick on purpose. Fire Orange is a little lighter, much more muted, warmer than Legendary Red.

Can I use Fire Orange instead of Legendary Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Fire Orange is a little lighter, much more muted, warmer than Legendary Red.

Can I use Legendary Red instead of Fire Orange?

The same difference applies the other way round: Legendary Red is a little darker, much 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.