Medium Rust vs Ryza Rust

How close are they?

ΔE 8.3, close: similar, with a visible difference side by side. Ryza Rust is a little darker, more saturated than Medium Rust.

Can I use Ryza Rust instead of Medium Rust?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Ryza Rust is a little darker, more saturated than Medium Rust.

Can I use Medium Rust instead of Ryza Rust?

The same difference applies the other way round: Medium Rust is a little lighter, more muted.

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.