ΔE 8.4, close: similar, with a visible difference side by side. Siena is more muted, cooler than Molten Orange. They are different kinds of paint: Army Painter Molten Orange 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.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Siena is more muted, cooler than Molten Orange. They are different kinds of paint.
The same difference applies the other way round: Molten Orange is more saturated, 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.
See Molten Orange on the colour wheel See Siena on the colour wheel
All matches: Molten Orange equivalents · Siena equivalents