Old Rust vs Light Rust

How close are they?

ΔE 7.5, close: similar, with a visible difference side by side. Light Rust is a little lighter, more muted than Old Rust.

Can I use Light Rust instead of Old Rust?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Light Rust is a little lighter, more muted than Old Rust.

Can I use Old Rust instead of Light Rust?

The same difference applies the other way round: Old Rust is a little darker, 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.