color: Support CSS color definitions

color: Support CSS color definitions

The CSS Color Module 3, available at:

  http://www.w3.org/TR/css3-color/

allows defining colors as:

  rgb ( r, g, b )
  rgba ( r, g, b, a)

along with the usual hexadecimal and named notations.

The r, g, and b channels can be:

  • integers between 0 and 255
  • percentages, between 0% and 100%

The alpha channel, if included using the rgba() modifier, can be a
floating point value between 0.0 and 1.0.

The ClutterColor parser should support this notation.