Demon Red vs Inferno Orange

How close are they?

ΔE 16.6, loose: different enough that you should pick on purpose. Inferno Orange is a little lighter, much more muted than Demon Red.

Can I use Inferno Orange instead of Demon Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Inferno Orange is a little lighter, much more muted than Demon Red.

Can I use Demon Red instead of Inferno Orange?

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

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.