Radiation Glow vs Ryza Rust

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Ryza Rust is a little darker than Radiation Glow.

Can I use Ryza Rust instead of Radiation Glow?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Ryza Rust is a little darker than Radiation Glow.

Can I use Radiation Glow instead of Ryza Rust?

The same difference applies the other way round: Radiation Glow is a little lighter.

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.