Archangel Red vs Fire Orange

How close are they?

ΔE 24.3, loose: different enough that you should pick on purpose. Fire Orange is a little lighter, much more muted, warmer than Archangel Red.

Can I use Fire Orange instead of Archangel Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Fire Orange is a little lighter, much more muted, warmer than Archangel Red.

Can I use Archangel Red instead of Fire Orange?

The same difference applies the other way round: Archangel 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.