The difference is that a morph male would add something to the morph female. For example, if you bred your normal male to a bumblebee female the best you could hope for would be bumblebee's. If you were to invest in a Pastel male and bred him to the Bumblebee female you have a chance of producing Killer Bees. You can breed him with normal females as well to produce normals and Pastels.