RLM 23 Red vs Devil Red

How close are they?

ΔE 22.7, loose: different enough that you should pick on purpose. Devil Red is noticeably lighter, more saturated, cooler than RLM 23 Red.

Can I use Devil Red instead of RLM 23 Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Devil Red is noticeably lighter, more saturated, cooler than RLM 23 Red.

Can I use RLM 23 Red instead of Devil Red?

The same difference applies the other way round: RLM 23 Red is noticeably darker, more muted, warmer.

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.