Inner Light vs Sandy Tan

How close are they?

ΔE 23.9, loose: different enough that you should pick on purpose. Sandy Tan is noticeably darker, much more muted than Inner Light.

Can I use Sandy Tan instead of Inner Light?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Sandy Tan is noticeably darker, much more muted than Inner Light.

Can I use Inner Light instead of Sandy Tan?

The same difference applies the other way round: Inner Light is noticeably lighter, much more saturated.

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.