Terran Khaki vs IDF Sand Grey

How close are they?

ΔE 9.3, close: similar, with a visible difference side by side. IDF Sand Grey is a little darker, more muted than Terran Khaki.

Can I use IDF Sand Grey instead of Terran Khaki?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). IDF Sand Grey is a little darker, more muted than Terran Khaki.

Can I use Terran Khaki instead of IDF Sand Grey?

The same difference applies the other way round: Terran Khaki is a little lighter, more saturated.

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.