IDF Sand Grey '73 vs Baneblade Brown

How close are they?

ΔE 7.6, close: similar, with a visible difference side by side. Baneblade Brown is a little darker, warmer than IDF Sand Grey '73.

Can I use Baneblade Brown instead of IDF Sand Grey '73?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Baneblade Brown is a little darker, warmer than IDF Sand Grey '73.

Can I use IDF Sand Grey '73 instead of Baneblade Brown?

The same difference applies the other way round: IDF Sand Grey '73 is a little lighter, 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.