The first to letters represent the intensity of the red color 00 is the less and ff the most intense.
So to get the color red the code will look like this:#FF0000.
The third and fourth symbols refer to the intesity of green color and the two last for blue.
Green:#00FF00.Blue:#0000FF.Here are some html color codes:
You can find all basic html color codes on: http://htmlcolorcodechart.blogspot.com.es/