Mini comics is not really mini. Basically it's a self-publish type of comic drawn on a 8-1/2x11 paper. Mini comics can be black and white or in color, either way just create your best if you want publishers to notice you. The number one reason to do a mini comic is to pimp your talent to publishers or to self-publish and sell your own comics to people.
Click here to go to a tutorial site on how to make your own mini comics.