(PHP 3 >= 3.0.2, PHP 4, PHP 5)
Get the index of the specified color or its closest possible
( resource image, int red, int green, int blue )
This function is guaranteed to return a color index for a
requested color, either the exact color or the closest possible
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().