liens : http://www.html-color-chart.com/ feuille excel
In the HTML language, colors are identified using the additive RGB (red, green, blue) color system. In this system, a color's red, green, and blue light intensities are each specified using 2 hexadecimal digits (8 bits). This scheme allows for 256 red, green, and blue intensity levels — for a total of 16,777,216 possible colors!
For example, full intensity red – ff – with no green or blue intensity produces the color red, which is coded as ff0000. Full intensities of red and green – ffff – with no blue intensity produces the color yellow, coded as ffff00. Full intensities of red, green, and blue produce white, which is coded ffffff.