Color properties and the history of pigments can be rather fascinating. Pigment through the Ages is a website that allows you to learn more about certain colors by clicking on certain colors.. I also find the color rotate feature a fascinating tool,because it allows you to play around with sets of color palettes. A nice tool to determine what color combinations might work well together.
What is really cool about this site is that it will give you a detailed description about each pigment, the names it is known by and even a sample artwork, where the paint was used in.