Colors can be defined using the red-green-blue (RGB) model in two ways:
 
Hexadecimal notation #RRGGBB and #RGB

“#”, followed by six hexadecimal characters (0-9, A-F).
“#”, followed by three hexadecimal characters (0-9, A-F).

The three-digit RGB notation (#RGB) and the six-digit form (#RRGGBB) are equal.
For example, #f03 and #ff0033represent the same color.
Functional Notation rgb(R,G,B)
“rgb”, followed by three or three values.
The integer number 255 corresponds to 100%, and to F or FF in the hexadecimal notation.

#f03
 #F03
 #ff0033
 #FF0033
 rgb(255,0,51)
 rgb(255, 0, 51)
 rgb(255, 0, 51.2) /* ERROR! Don't use fractions, use integers */ 
 rgb(100%,0%,20%)
 rgb(100%, 0%, 20%)
 rgb(100%, 0, 20%) /* ERROR! Don't mix up integer and percentage notation */