There are a fair number of You tube videos demonstrating car paints that change colours. Some of these are pranks or Hoaxes that have had digital footage edited in a computer program such as a Adobe. These edits have been done so well that many have fallen for the trick including some well respected auto bloggers. There is also some fairly old technology out there that does actually show cars paint changing colour. The videos that are not a hoax are vehicles that change colours based of the temperature of the paint. Its called Thermochromic dye or ink and is somewhat fascinating. In the video you can see hot water is poured on the cars paint work. The large change in temperature allows the vehicle to change colour. Check out the video.
How does it work? Source: explainthatstuff.com
Sometimes we want things to change colour as they get hotter or colder just for novelty or entertainment—and we don’t need anything as sophisticated as a TLC for that. You’ve probably seen those coffee cups with hidden messages or pictures that suddenly appear, like magic, as you fill them with hot water? Or maybe you have a T-shirt or a poster that changes colour when you touch it? Things like this are printed with special temperature-sensitive dyes (or inks) called leucodyes, which start off transparent (or have a particular colour) and become visible (or change to a different colour) as the temperature rises or falls.
Leucodyes are organic (carbon-based) chemicals that change colour when heat energy makes their molecules shift back and forth between two subtly differently structures—known as the leuco (colourless) and non-leuco (coloured) forms. The leuco and non-leuco forms absorb and reflect light differently, so appear very different colours when printed on a material such as paper or cotton.
Photo: Left: Temperature-sensitive printing: the promotional competition sticker I’ve stuck to this cup is designed to change colour when its temperature changes. Put it against a cold cup and the whole thing looks black. Add boiling water to the cup and the black background ink (printed with a leucodye) turns white, revealing a hidden message printed in normal black ink. Did I win the competition this time? Nope!
Unlike TLCs, which shift color up and down the red-violet spectrum as they get hotter or colder, leucodyes can be mixed in various ways to produce all kinds of color-changing effects at a wide range of everyday temperatures. Leucodyes are much cruder indicators of temperature than TLCs, generally just indicating “cold” versus “hot” with one simple colour change. That’s because all can they do is switch back and forth between their two different forms (leuco and non-leuco). Like TLCs, leucodyes can be printed on the surface of other materials in the form of microscopic capsules, but they can be produced more easily with traditional printing methods such as screenprinting. That’s why leucodyes are more widely used in mass-produced, everyday, novelty items than TLCs, which tend to require special printing equipment. Leucodyes are also used to make thermal computer printer paper (the slippery, curly paper used in checkout receipts that fades quite quickly in sunlight) and in “hypercolor” t-shirts that change color when you touch them.
Watch out for the hoax videos that claim vehicles can change through multiple colours using some electrical gizmo in the car. Its not real but still worth the watch. check it out here.