Red Lorry Yellow Lorry

Now why is it that these two lorries appear to us so different?
They are both made of metal. They both have coats of paint. But why do the coats of paint hit our eyeballs in such strangely different ways. It must be a chemistry thing. What is it that makes one so markedly different from the other. What is it about the surface of each lorry that incites us to see it as different from other lorries. OK. We know that different colours travel on different wave-lengths. Hence..put white light through a prism and it will split into its various wave-length counterparts..........red orange yellow green blue indigo and violet. But I don't understand the way that different surfaces/substances/products exude such different colours.