Vampire Red vs Rust Orange

How close are they?

ΔE 18.9, loose: different enough that you should pick on purpose. Rust Orange is noticeably lighter, warmer than Vampire Red.

Can I use Rust Orange instead of Vampire Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Rust Orange is noticeably lighter, warmer than Vampire Red.

Can I use Vampire Red instead of Rust Orange?

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