Slaughter Red vs Rust

How close are they?

ΔE 23.8, loose: different enough that you should pick on purpose. Rust is a little lighter, warmer than Slaughter Red.

Can I use Rust instead of Slaughter Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Rust is a little lighter, warmer than Slaughter Red.

Can I use Slaughter Red instead of Rust?

The same difference applies the other way round: Slaughter Red is a little 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.