Green Sun vs Radiant Yellow

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Radiant Yellow is more saturated than Green Sun.

Can I use Radiant Yellow instead of Green Sun?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Radiant Yellow is more saturated than Green Sun.

Can I use Green Sun instead of Radiant Yellow?

The same difference applies the other way round: Green Sun is 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.