To specify a color on a web page, you have to use the RGB mode to determine it. The method is to specify R/G/B, that is, the intensity of the three primary colors red/green/blue respectively. It is usually stipulated that the intensity of each color is from 0 to 255, and is usually expressed in hexadecimal values. Then 255 corresponds to FF in hexadecimal, and the three values ​​are listed in sequence, starting with #.

For example, the color value "#FF0000" is red, because the value of red reaches the maximum value FF (that is, 255 in decimal), and the intensities of the other two colors are 0. For example, "#FFFF00" represents yellow, because when red and green are both at their maximum values ​​and blue is 0, yellow is produced.