Description
int 
imagecolorexact ( resource image, int red, int green, int blue )
    Returns the index of the specified color in the palette of the
    image.
   
    If the color does not exist in the image's palette, -1 is
    returned.
   
    If you created the image from a file, only colors used in the image are
    resolved. Colors present only in the pallete are not resolved.
   
    See also imagecolorclosest().