it depends on the theme for me. The superman rides at the six flags parks have a good colour scheme for the theme, in that case i like the multicoloured track. But for rides like air, or rita, i don't think more than one colour would work.
The colour scheme fits the ride, but it still looks god awful! Generally, i dont think its the different colours, but more the subtlety and contrast of the colours, none of the rides at AT are down with bright outstanding colours, all are done with subtle, pleasing tones which look great IMO. UK rides in general (excluding fairground rides) do.