Tiamat Orange vs Gold Yellow

How close are they?

ΔE 6.4, close: similar, with a visible difference side by side. Gold Yellow is more saturated than Tiamat Orange.

Can I use Gold Yellow instead of Tiamat Orange?

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

Can I use Tiamat Orange instead of Gold Yellow?

The same difference applies the other way round: Tiamat 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.