Beige Grey vs IAF Sand

How close are they?

ΔE 6.7, close: similar, with a visible difference side by side. IAF Sand is more saturated, cooler than Beige Grey.

Can I use IAF Sand instead of Beige Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). IAF Sand is more saturated, cooler than Beige Grey.

Can I use Beige Grey instead of IAF Sand?

The same difference applies the other way round: Beige Grey is 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.