Parts of the pieces are already painted, but if you take notice it's only the parts that will be touching other parts (i.e. where the support meets the track). That much is precision work, which is why it's done. The rest is by far easier to paint the assembled ride. Especially given the fact that by nature of construction, there are bound to be scratches and chips in the paint anyway, so rather than paint-build-touchup, it's more cost effective to build-paint-lookgreat. :)