Poppy Red vs Rust

How close are they?

ΔE 20.3, loose: different enough that you should pick on purpose. Rust is a little darker, more muted, warmer than Poppy Red.

Can I use Rust instead of Poppy Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Rust is a little darker, more muted, warmer than Poppy Red.

Can I use Poppy Red instead of Rust?

The same difference applies the other way round: Poppy Red is a little lighter, 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.