Moonstone Grey vs Sand

How close are they?

ΔE 15.2, loose: different enough that you should pick on purpose. Sand is noticeably darker, more saturated than Moonstone Grey.

Can I use Sand instead of Moonstone Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Sand is noticeably darker, more saturated than Moonstone Grey.

Can I use Moonstone Grey instead of Sand?

The same difference applies the other way round: Moonstone Grey is noticeably lighter, more muted.

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.