Fiendish Yellow vs Golden Brown

How close are they?

ΔE 7.8, close: similar, with a visible difference side by side. Golden Brown is more muted than Fiendish Yellow.

Can I use Golden Brown instead of Fiendish Yellow?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Golden Brown is more muted than Fiendish Yellow.

Can I use Fiendish Yellow instead of Golden Brown?

The same difference applies the other way round: Fiendish Yellow is more saturated.

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.