IDF Sand Grey '73 vs Ionrach Skin

How close are they?

ΔE 6.9, close: similar, with a visible difference side by side. Ionrach Skin is warmer than IDF Sand Grey '73.

Can I use Ionrach Skin instead of IDF Sand Grey '73?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Ionrach Skin is warmer than IDF Sand Grey '73.

Can I use IDF Sand Grey '73 instead of Ionrach Skin?

The same difference applies the other way round: IDF Sand Grey '73 is cooler.

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.