From Forum Nokia Wiki

Old days most computers only supported 256 different colors, on those days were created a list of 216 Web Safe Colors. Today computers have the ability to display more colours, but there still can be devices which need this. The 216 color palette was created to ensure that all computers would display the colors correctly when running a 256 color palette. Also if you validate your code with W3C validator, there is listed only color names for 16 different colour. So others need to specify using the HEX or RGB values. Those 16 ones are aqua, black, blue, fuchsia, gray, green, lime, maroon, navy, olive, purple, red, silver, teal, white, and yellow

Example page http://www.techbomb.com/websafe/ you can find the list of the 216 Web Safe color