This function is guaranteed to return a color index for a requested color, either the exact color or the closest possible alternative.
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.