ColorKey ( ImageSlot, Color )
Sets the color key of a given image slot to a 32-Bit color value.
NOTE: COLORKEY IS A PIXEL OPERATION PERFORM BY THE CPU SO YOU SHOULD
NOT USE IT DURING SPEED CRITICAL MOMENTS
Example:
ColorKey ( 0, RGB ( 255, 255, 255 ) )
This uses the RGB function to return the 32-Bit value of the color white and
sets the color as the color key of image slot 0.