Stone Grey vs Terran Khaki

How close are they?

ΔE 8.3, close: similar, with a visible difference side by side. Terran Khaki is a little darker, more saturated, cooler than Stone Grey.

Can I use Terran Khaki instead of Stone Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Terran Khaki is a little darker, more saturated, cooler than Stone Grey.

Can I use Stone Grey instead of Terran Khaki?

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