Returns the index of the color in the palette of the image which is "closest" to the specified RGB value and alpha level.
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 indicates completely opaque while
127 indicates completely transparent.
The colors parameters are integers between 0 and 255 or hexadecimals between 0x00 and 0xFF.