Rock Grey vs Terminatus Stone

How close are they?

ΔE 6.2, close: similar, with a visible difference side by side. Terminatus Stone is a little lighter than Rock Grey.

Can I use Terminatus Stone instead of Rock Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Terminatus Stone is a little lighter than Rock Grey.

Can I use Rock Grey instead of Terminatus Stone?

The same difference applies the other way round: Rock Grey is a little darker.

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.