Carmine Dragon vs Rust

How close are they?

ΔE 41.2, loose: different enough that you should pick on purpose. Rust is a little darker, much more muted, warmer than Carmine Dragon.

Can I use Rust instead of Carmine Dragon?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 41). Rust is a little darker, much more muted, warmer than Carmine Dragon.

Can I use Carmine Dragon instead of Rust?

The same difference applies the other way round: Carmine Dragon is a little lighter, 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.