Imperial Red vs Demon Red

How close are they?

ΔE 16.4, loose: different enough that you should pick on purpose. Demon Red is noticeably lighter, more muted than Imperial Red.

Can I use Demon Red instead of Imperial Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Demon Red is noticeably lighter, more muted than Imperial Red.

Can I use Imperial Red instead of Demon Red?

The same difference applies the other way round: Imperial Red is noticeably darker, 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.