Returns the index of the specified color+alpha in the palette of the image.
An image resource, returned by one of the image creation functions, such as imagecreatetruecolor().
Value of red component
Value of green component
Value of blue component
A value between 0 and 127. 0 indicates completely opaque while 127 indicates completely transparent.
Returns the index of the specified color+alpha in the palette of the image, or -1 if the color does not exist in the image's palette.