Parses a textual specification of a color and fill in the red, green, and
blue fields of a Color structure. The color is not allocated,
you must call alloc_color yourself. The string can either one of a large
set of standard names. (Taken from the X11 rgb.txt file), or it can be a hex value in the form '#rgb' '&
num;rrggbb' '#rrrgggbbb' or '#rrrrggggbbbb' where 'r', 'g' and 'b' are hex digits of the red, green, and blue
components of the color, respectively. (White in the four forms is '#fff' '#ffffff' '#fffffffff' and '&
num;ffffffffffff')
Returns a textual specification of color in the hexadecimal form #rrrrggggbbbb
, where r, g and b are hex digits representing the red, green and blue components respectively.