Japanese Brown vs T'au Light Ochre

How close are they?

ΔE 7.7, close: similar, with a visible difference side by side. T'au Light Ochre is a little darker than Japanese Brown.

Can I use T'au Light Ochre instead of Japanese Brown?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). T'au Light Ochre is a little darker than Japanese Brown.

Can I use Japanese Brown instead of T'au Light Ochre?

The same difference applies the other way round: Japanese Brown is a little lighter.

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.