CSS offers you a variety of ways to specify the color you want for an element, such as: font color, borders, backgrounds etc. Plus with CSS3 you can also specify an opacity level for your colors, when using the RGBA or HSLA color format, more on this later. CSS colors are defined using a hexadecimal (hex) notation for the combination of Red, Green, and Blue color values (RGB). The lowest value that can be given to one of the light sources is 0 (hex 00). The highest value is 255 (hex FF).

Color values can be written in the following formats:

#RRGGBB This is a hex-pair notation using in traditional HTML. In this format, the first pair of digits corresponds to the red level, the second pair to the green, and the third pair to the blue. Each pair is in hexadecimal notation in the range 00-FF. Thus, a pure blue is written #0000FF, a pure red is written #FF0000, and so on.

#RGB This is a shorter form of the six-digit notation described previously. In this format, each digit is replicated to arrive at an equivalent six-digit value; thus, #F8C becomes #FF88CC.

rgb(rrr,ggg,bbb) This format allows the author to use RGB values in the range 0-255; only integers are permitted. Not coincidentally, this range is the decimal equivalent of 00-FF in hexadecimal. In this format, pure green is rgb (0,255,0), and white is represented as rgb (255,255,255).

rgb(rrr.rr%,ggg.gg%,bbb.bb%) This format allows the author to use RGB values in the range 0% to 100%, with decimal values allowed (e.g., 75.5%). The value for black is thus rgb (0%,0%,0%),whereas pure blue is rgb (0%,0%,100%).

HSL or HSLA(hhh.hh,sss.ss%,lll.ll%) This format permits authors to specify a color by its hue angle, saturation, and lightness (thus HSL). The hue angle is always a unitless number in the range 0 to 360 and the saturation and brightness values are always percentages. Hue angles 0 and 360 are equivalent, and are both red. Hue angles greater than 360 can be declared but they are normalized to the 0360 range; thus, setting a hue angle of 454 is equivalent to setting an angle of 94. Any HSL value, regardless of color angle, will be rendered as a shade of gray if the saturation value is 0%; the exact shade will depend on the lightness value. Any HSL value, regardless of the hue angle, will be rendered solid black if lightness is 0% and solid white if lightness is 100%. The normal lightness valuethat is, the value associated with most common colorsis 50%.