By 1981, computers could put a shine on anything, and so many shiny things they drew looked like plastic. Every highlight was drawn the colour of the light, white, on a coloured body. That is exactly how real plastic works: clear stuff with coloured grains inside. More shine only makes better plastic. At Cornell, Robert Cook and Kenneth Torrance looked at what metal really does. Light barely gets in; it reflects "essentially at the surface", so metal has no coloured body at all. Gold sends back about 96 % of red light and only 41 % of blue (our arithmetic from Johnson and Christy's measurements). So take the colour out of the body and put it in the reflection: "The specular component is usually the color of the material, not the color of the light source." Gold is a mirror that turns the whole world gold. Pixar ray-traced Cars partly for its reflections, "an important visual cue to the shape and material of the car", and Disney made metal one dial, metallic, for Wreck-It Ralph. And tilt anything smooth far enough and it turns into a mirror: plastic reflects about 4 % head-on and nearly everything at a grazing angle. Even gold goes white there.

The spheres, toy car and world here are our own recreations, not images from any film.

Which movie trick should we take apart next?

Sources: Robert L. Cook and Kenneth E. Torrance, "A Reflectance Model for Computer Graphics", SIGGRAPH 1981 and ACM Transactions on Graphics 1982; Brent Burley, "Physically Based Shading at Disney", SIGGRAPH 2012 course notes (Wreck-It Ralph); Naty Hoffman, "Background: Physics and Math of Shading", SIGGRAPH 2012 course; Christensen, Fong, Laur and Batali, "Ray Tracing for the Movie 'Cars'", IEEE Interactive Ray Tracing 2006 (Pixar); Johnson and Christy, "Optical Constants of the Noble Metals", Physical Review B 1972.
Sounds: our own, made in code (earshot, CC0).