Dark Sun Yellow vs Flat Flesh

How close are they?

ΔE 9.7, close: similar, with a visible difference side by side. Flat Flesh is a little lighter, more saturated, warmer than Dark Sun Yellow.

Can I use Flat Flesh instead of Dark Sun Yellow?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Flat Flesh is a little lighter, more saturated, warmer than Dark Sun Yellow.

Can I use Dark Sun Yellow instead of Flat Flesh?

The same difference applies the other way round: Dark Sun Yellow is a little darker, more muted, cooler.

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.