ΔE 5.0, very close: most people won’t see a difference side by side. Siena is a little darker than Ruddy Terra. They are different kinds of paint: Army Painter Ruddy Terra is an opaque base/layer paint and Green Stuff World Siena is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Yes, for most jobs. Very close match (ΔE 5). Siena is a little darker than Ruddy Terra. They are different kinds of paint.
The same difference applies the other way round: Ruddy Terra 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 Ruddy Terra on the colour wheel See Siena on the colour wheel
All matches: Ruddy Terra equivalents · Siena equivalents