Sand FS 33531 vs Terminatus Stone

How close are they?

ΔE 7.2, close: similar, with a visible difference side by side. Terminatus Stone is a little lighter, cooler than Sand FS 33531.

Can I use Terminatus Stone instead of Sand FS 33531?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Terminatus Stone is a little lighter, cooler than Sand FS 33531.

Can I use Sand FS 33531 instead of Terminatus Stone?

The same difference applies the other way round: Sand FS 33531 is a little darker, 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.