Dark Yellow vs Sand Yellow

How close are they?

ΔE 18.9, loose: different enough that you should pick on purpose. Sand Yellow is a little lighter, much more saturated, warmer than Dark Yellow.

Can I use Sand Yellow instead of Dark Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Sand Yellow is a little lighter, much more saturated, warmer than Dark Yellow.

Can I use Dark Yellow instead of Sand Yellow?

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