ΔE 11.5, fair: the same colour family, but not a straight swap. Raw Sienna is a little darker than T'au Light Ochre. They are different kinds of paint: Citadel T'au Light Ochre is an opaque base/layer paint and Golden Raw Sienna is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Raw Sienna is a little darker than T'au Light Ochre. They are different kinds of paint.
The same difference applies the other way round: T'au Light Ochre 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.
See T'au Light Ochre on the colour wheel See Raw Sienna on the colour wheel
All matches: T'au Light Ochre equivalents · Raw Sienna equivalents