Flesh Tearers Red vs Rust

How close are they?

ΔE 21.8, loose: different enough that you should pick on purpose. Rust is much more muted, warmer than Flesh Tearers Red.

Can I use Rust instead of Flesh Tearers Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Rust is much more muted, warmer than Flesh Tearers Red.

Can I use Flesh Tearers Red instead of Rust?

The same difference applies the other way round: Flesh Tearers Red is 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.