CSS uses color values to specify a color. Typically, these are used to set a color either for the foreground of an element (i.e., its text)
or else for the background of the element. They can also be used to affect the color of borders and other decorative effects.
You can specify your color values in various formats :

• Hex Code
• Short Hex Code
• RGB %
• RGB Absolute
• keyword
  

  Hex Codes :
  

  A hexadecimal is a 6 digit representation of a color. The first two digits(RR) represent a red value,
   the next two are a green value(GG), and the last are the blue value(BB).
  

  
  Short Hex Codes :

  This is a shorter form of the six-digit notation. In this format, each digit is replicated to arrive at
  an equivalent six-digit value. For example: #6A7 becomes #66AA77.

   RGB Values :

  This color value is specified using the rgb( ) property. This property takes three values,
  one each for red, green, and blue. The value can be an integer between 0 and 255 or a percentage.

  
  

  Type	Syntax	Demo
  Hex Code	#RRGGBB	p{color:#FF0000;}
  Short Hex Code	#RGB	p{color:#6A7;}
  RGB %	rgb(rrr%,ggg%,bbb%)	p{color:rgb(50%,50%,50%);}
  RGB Absolute	rgb(rrr,ggg,bbb)	p{color:rgb(0,0,255);}
  keyword	aqua, black, etc.	p{color:teal;}