Grey Brown vs Sand

How close are they?

ΔE 6.6, close: similar, with a visible difference side by side. Sand is a little darker than Grey Brown.

Can I use Sand instead of Grey Brown?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Sand is a little darker than Grey Brown.

Can I use Grey Brown instead of Sand?

The same difference applies the other way round: Grey Brown is a little lighter.

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.