Ryza Rust vs Raw Sienna

How close are they?

ΔE 9.9, close: similar, with a visible difference side by side. Raw Sienna is a little darker, more muted than Ryza Rust.

Can I use Raw Sienna instead of Ryza Rust?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Raw Sienna is a little darker, more muted than Ryza Rust.

Can I use Ryza Rust instead of Raw Sienna?

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

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.