Radium vs Radiant Yellow

How close are they?

ΔE 9.3, close: similar, with a visible difference side by side. Radiant Yellow is a little darker, more saturated, warmer than Radium.

Can I use Radiant Yellow instead of Radium?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Radiant Yellow is a little darker, more saturated, warmer than Radium.

Can I use Radium instead of Radiant Yellow?

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

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.