The first 2 digits in the RGB color code denote red, the second 2 green and the last 2 blue. Each number denotes the strength of that particular color - FF0000 is only red (no green, no blue), 00FF00 only green (no red, no blue). If all colors are present in equal strength FFFFFF, you get white, if no color is present 000000, black.
Ubiquity is a new Firefox plugin that can be used as a command line for creating simple Web mashups. Check this simple tutorial on how to write a new Ubiquity command.