Why can red-orange made by layering transparent red and orange paint look different from red-orange made by mixing the paints directly?

Correct answer: Layering combines the colours optically, while direct mixing combines the pigments physically

With transparent paint layers, light passes through the coloured films and interacts with the surface beneath them; the colours are perceived together. Direct mixing combines pigment particles in one paint mixture, changing how the mixture absorbs and scatters light. The result can therefore differ, depending on factors such as transparency, layer order, and the underlying surface.