Bright Orange vs Sun Yellow

How close are they?

ΔE 9.2, close: similar, with a visible difference side by side. Sun Yellow is more saturated than Bright Orange.

Can I use Sun Yellow instead of Bright Orange?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Sun Yellow is more saturated than Bright Orange.

Can I use Bright Orange instead of Sun Yellow?

The same difference applies the other way round: Bright Orange 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.