Sandy Tan vs Sand Yellow

How close are they?

ΔE 18.1, loose: different enough that you should pick on purpose. Sand Yellow is noticeably lighter, much more saturated, cooler than Sandy Tan.

Can I use Sand Yellow instead of Sandy Tan?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Sand Yellow is noticeably lighter, much more saturated, cooler than Sandy Tan.

Can I use Sandy Tan instead of Sand Yellow?

The same difference applies the other way round: Sandy Tan is noticeably darker, much more muted, 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.