T'au Light Ochre vs Peanut Butter

How close are they?

ΔE 8.8, close: similar, with a visible difference side by side. Peanut Butter is cooler than T'au Light Ochre.

Can I use Peanut Butter instead of T'au Light Ochre?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Peanut Butter is cooler than T'au Light Ochre.

Can I use T'au Light Ochre instead of Peanut Butter?

The same difference applies the other way round: T'au Light Ochre is 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.