Wrack White vs Sand Grey

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. Sand Grey is noticeably darker, more saturated than Wrack White.

Can I use Sand Grey instead of Wrack White?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Sand Grey is noticeably darker, more saturated than Wrack White.

Can I use Wrack White instead of Sand Grey?

The same difference applies the other way round: Wrack White 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.