Re: How does heat-sensitive plastic work?

     Almost all plastics have something in them to make them colored; we 
call them "pigments" or "dyes". For the plastics that change color when 
the temperature changes, the stuff used to color them has a special 
property. Have you ever seen a crystal hanging in the sunlight? As it 
turns, you see different colors. What happens to the pigment used to color 
the plastic is sort of like that. At one temperature, the light it 
reflects back to you is one color, but when the temperature changes, the 
pigment's structure changes (sort of like the turning crystal) so that it 
reflects back a different color. Different chemicals are used to get 
different colors, or to make the color change happen at different 
temperatures.