Dark Sun Yellow vs Green Ochre

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. Green Ochre is a little darker, more muted, cooler than Dark Sun Yellow.

Can I use Green Ochre instead of Dark Sun Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Green Ochre is a little darker, more muted, cooler than Dark Sun Yellow.

Can I use Dark Sun Yellow instead of Green Ochre?

The same difference applies the other way round: Dark Sun Yellow is a little lighter, 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.