One part at a time. First of all, this is a pretty major project to just 'try at home'. The materials and the process for doing this are not just hard-to-find, but difficult to do successfully without special equipment.
Zinc sulfide and copper are only one of many mixtures that will work. The important point is that you have a 'phosphor' (like zinc sulfide) with other stuff mixed in. I don't know the exact
proportions, but they use a large amount of the zinc sulfide and 'dope' it with just a little bit of copper (or whatever else they're using). 'Doping' is a technical word that basically means 'mixing in just a little bit'.
The whole mixture gets pressed between two electrodes (the top one of which is transparent) and hooked up to an alternating current (AC). When the power is turned on, it creates a strong electric field that activates the dopant (the stuff that's mixed in), making it produce light.
A great picture of how this all goes together (along with most of the information I've got here) comes from Britannica Online
Your second question is easier... Depending on which dopant you use, you'll get different colors. For example, a mixture of copper and chlorine gives blue light. Copper and aluminum make green light. And copper, chlorine, and manganese together make yellow.
To make something that can switch between two different colors, all they have to do is make two sets of layers. One is made with copper and chlorine, for example, and another with copper and aluminum. Each layer has a separate pair of electrode layers and each one is hooked up to a separate alternating current. Flipping the switch just changes which 'sandwich' gets turned on.
(republished on 07/28/06)