Black Rose Immortal vs Light Rust

How close are they?

ΔE 7.4, close: similar, with a visible difference side by side. Light Rust is a little lighter, more saturated than Black Rose Immortal.

Can I use Light Rust instead of Black Rose Immortal?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Light Rust is a little lighter, more saturated than Black Rose Immortal.

Can I use Black Rose Immortal instead of Light Rust?

The same difference applies the other way round: Black Rose Immortal is a little darker, 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.