imagecolorallocate() returns a
color identifier representing the color composed of the given
RGB components. The im argument is the return from the
imagecreate() function.
red, green and blue are the values of the red,
green and blue component of the requested color respectively.
These parameters are integers between 0 and 255. imagecolorallocate() must be called to create
each color that is to be used in the image represented by image.
Returns -1 if the allocation failed.