Walnut vs German Dark Yellow

How close are they?

ΔE 6.8, close: similar, with a visible difference side by side. German Dark Yellow is a little lighter, more muted, cooler than Walnut.

Can I use German Dark Yellow instead of Walnut?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). German Dark Yellow is a little lighter, more muted, cooler than Walnut.

Can I use Walnut instead of German Dark Yellow?

The same difference applies the other way round: Walnut is a little darker, more saturated, warmer.

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.