Tallarn Sand vs Dark Sun Yellow

How close are they?

ΔE 7.6, close: similar, with a visible difference side by side. Dark Sun Yellow is a little lighter than Tallarn Sand.

Can I use Dark Sun Yellow instead of Tallarn Sand?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Dark Sun Yellow is a little lighter than Tallarn Sand.

Can I use Tallarn Sand instead of Dark Sun Yellow?

The same difference applies the other way round: Tallarn Sand is a little darker.

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.